BACKGROUND AND PURPOSE The transcriptional co-activator with PDZ-binding motif (TAZ) is a key controller of mesenchymal stem cell differentiation through its nuclear localization and subsequent interaction with master transcription factors. In particular, TAZ directly associates with myoblast determining protein D (MyoD) and activates MyoD-induced myogenic gene expression, thereby enhancing myogenic differentiation. Here, we have synthesized and characterized low MW compounds modulating myogenic differentiation via induction of TAZ nuclear localization. EXPERIMENTAL APPROACH COS7 cells stably transfected with GFP-TAZ were used in a high content imaging screen for compounds specifically enhancing nuclear localization of TAZ. We then studied the effects of such TAZ modulators on myocyte differentiation of C2C12 cells and myogenic transdifferentiation of mouse embryonic fibroblast cells in vitro and muscle regeneration in vivo. KEY RESULTS We identified two TAZ modulators, TM-53, and its structural isomer, TM-54. Each compound strongly enhanced nuclear localization of TAZ by reducing S89-phosphorylation and dose-dependently augmented myogenic differentiation and MyoD-mediated myogenic transdifferentiation through an activation of MyoD-TAZ interaction. The myogenic stimulatory effects of TM-53 and TM-54 were impaired in the absence of TAZ, but retrieved by the restoration of TAZ. In addition, administration of TM-53 and TM-54 enhanced injury-induced muscle regeneration in vivo and attenuated myofiber injury in vitro. CONCLUSIONS AND IMPLICATIONS The novel TAZ modulators TM-53 and TM-54 accelerated myogenic differentiation and improved muscle regeneration and function after injury, demonstrating that low MW compounds targeting the nuclear localization of TAZ have beneficial effects in skeletal muscle regeneration and in recovery from muscle degenerative diseases. Abbreviations DEX, dexamethasone; KO, knockout; KRICT, Korea Research Institute of Chemical Technology; MAFbx, muscle atrophy F-box; MCK, muscle creatine kinase; MEF, mouse embryonic fibroblast; MRF, muscle regulatory factor; MuRF1, muscle-specific RING finger protein 1; MYF5, myogenic determination factor 5; MyHC, myosin heavy chain; MyoD, myoblast determining protein D; Myog, myogenine; RFP-H2B, red fluorescence protein-tagged histone 2B; TAZ, transcriptional co-activator with PDZ-binding motif; TM, TAZ modulator; WT, wild type BJP British Journal of Pharmacology

Cells sense and migrate across mechanically dissimilar environments throughout development and disease progression. However, it remains unclear whether mechanical memory of past environments empowers cells to navigate new, three-dimensional extracellular matrices. Here, we show that cells previously primed on stiff matrices, compared to soft, generate higher forces to remodel collagen fibers and promote invasion. This priming advantage persists in dense or stiffened collagen. We explain this memory-dependent cross-environment cell invasion through a lattice-based model wherein stiff-primed cellular forces remodel collagen and minimize energy required for future cell invasion. According to our model, cells transfer their mechanical memory to the matrix via collagen alignment and tension, and this remodeled matrix informs future cell invasion. Thus, memory-laden cells overcome mechanosensing of softer or challenging future environments via a cell-matrix transfer of memory. Consistent with model predictions, depletion of yes-associated protein destabilizes cellular memory required for collagen remodeling before invasion. We release tension in collagen fibers via laser ablation and disable fiber remodeling by lysyl-oxidase inhibition; both of which disrupt cell-to-matrix transfer of memory and hamper cross-environment invasion. These results have implications for cancer, fibrosis, and aging, where a potential cell-to-matrix transfer of mechanical memory of cells may generate prolonged cellular response. [Media: see text] [Media: see text] [Media: see text]

Cellular forces and intercellular cooperation generate collective cell migration. Pathological changes in cell-level genetic and physical properties cause jamming, unjamming, and scattering in epithelial migration. Separately, changes in microenvironment stiffness and confinement can produce varying modes of cell migration. However, it remains unclear whether and how mesoscale disruptions in matrix topology alter collective cell migration. To address this question, we microfabricated matrices with stumps of defined geometry, density, and orientation, which serve as obstructions in the path of collectively migrating healthy mammary epithelial cells. Here, we show that cells lose their speed and directionality when moving through dense obstructions, compared to those sparsely spaced. On flat surfaces, leader cells are significantly stiffer than follower cells, while dense obstructions lead to the overall softening of cells. In moving through dense obstructions, epithelial cells lose the sense of leaders and followers in their physical properties, migration phenotypes, and fluidity. Although Rac inhibition reduces obstruction sensitivity, loss of cell-cell cooperation and induction of leader-like phenotype via α-catenin depletion eliminates the effect of matrix obstructions on epithelial migration. Through a lattice-based model, we identify cellular protrusions, polarity, and leader-follower communication as key mechanisms for obstruction-sensitive collective cell migration. Together, microscale cytoskeletal response, mesoscale softening and disorder, and macroscale multicellular communication enable epithelial cell populations to sense topological obstructions encountered in challenging environments. These results reveal that cohesive, healthy populations are more obstruction sensitive than the dysfunctional, aggressive ones. The ‘obstruction-sensitivity’ could add to the emerging disease ‘mechanotypes’ such as cell stiffness and traction forces.

During disease and development, physical changes in extracellular matrix cause jamming, unjamming, and scattering in epithelial migration. However, whether disruptions in matrix topology alter collective cell migration speed and cell-cell coordination remains unclear. We microfabricated substrates with stumps of defined geometry, density, and orientation, which create obstructions for migrating epithelial cells. Here, we show that cells lose their speed and directionality when moving through densely spaced obstructions. While leader cells are stiffer than follower cells on flat substrates, dense obstructions cause overall cell softening. Through a lattice-based model, we identify cellular protrusions, cell-cell adhesions, and leader-follower communication as key mechanisms for obstruction-sensitive collective cell migration. Our modeling predictions and experimental validations show that cells’ obstruction sensitivity requires an optimal balance of cell-cell adhesions and protrusions. Both MDCK (more cohesive) and α-catenin depleted MCF10A cells were less obstruction sensitive than wildtype MCF10A cells. Together, microscale softening, mesoscale disorder, and macroscale multicellular communication enable epithelial cell populations to sense topological obstructions encountered in challenging environments. Thus, obstruction-sensitivity could define ‘mechanotype’ of cells that collectively migrate yet maintain intercellular communication.

Clinical research output in the emergency department (ED) continues to be constrained by limitations in funding for researchers, demands of patient care on ED providers, and difficulties in obtaining high‐quality data. In response, several institutions have established programs in which student volunteers are integrated into department workflows to increase clinical research output and introduce pre‐health students to careers in medicine. One such program, the student volunteer clinical research program, presently consists of over 40 undergraduate and post‐baccalaureate student volunteers who screen, consent, and enroll patients into prospective studies in the ED of the University of California, Los Angeles (UCLA) Ronald Reagan Medical Center. The program is led by student coordinators who collaborate with departmental research staff and faculty. Our program is unique in that it is primarily run by the students themselves. Experienced student research associates facilitate recruitment through a competitive biannual application process, train new volunteers to perform on‐shift research duties, and monitor participants for compliance with both hospital and program policies. Participation in the program provides students with exposure to frontline medical research, opportunities to observe clinical medicine, and access to a variety of program‐specific resources including student‐led committees, career development resources, and mentorship from peers, alumni, and faculty. This concept piece serves as a structural model for other institutions seeking to implement volunteer clinical research or bolster existing programs through increased student‐led initiatives.