Myofibroblast contraction activates latent TGF-β1 from the extracellular matrix

Abstract

The conjunctive presence of mechanical stress and active transforming growth factor β1 (TGF-β1) is essential to convert fibroblasts into contractile myofibroblasts, which cause tissue contractures in fibrotic diseases. Using cultured myofibroblasts and conditions that permit tension modulation on the extracellular matrix (ECM), we establish that myofibroblast contraction functions as a mechanism to directly activate TGF-β1 from self-generated stores in the ECM. Contraction of myofibroblasts and myofibroblast cytoskeletons prepared with Triton X-100 releases active TGF-β1 from the ECM. This process is inhibited either by antagonizing integrins or reducing ECM compliance and is independent from protease activity. Stretching myofibroblast-derived ECM in the presence of mechanically apposing stress fibers immediately activates latent TGF-β1. In myofibroblast-populated wounds, activation of the downstream targets of TGF-β1 signaling Smad2/3 is higher in stressed compared to relaxed tissues despite similar levels of total TGF-β1 and its receptor. We propose activation of TGF-β1 via integrin-mediated myofibroblast contraction as a potential checkpoint in the progression of fibrosis, restricting autocrine generation of myofibroblasts to a stiffened ECM.

Transforming Growth Factor β1 Function in Airway Remodeling and Hyperresponsiveness. The Missing Link?

“…Conversely, the act of ASM shortening alone activates TGF-b1 signaling. Agonist-induced ASM bronchoconstriction (22) and myofibroblast contraction (23) induce the release of active TGF-b1, which may augment both airway remodeling and airway narrowing. Furthermore, challenge with the contractile agonist methacholine induces active TGF-b1 release and airway remodeling without affecting airway eosinophil recruitment, suggesting an uncoupling of airway inflammation from both AHR and remodeling (24).…”

Stiffening hydrogels to probe short- and long-term cellular responses to dynamic mechanics

“…However, matrix stiffening is more relevant for many biological events, including tissue development, wound healing and disease progression, such as fibrosis and tumour formation. For instance, fibrous scar tissue that develops after myocardial infarction is much stiffer than normal myocardium [17][18][19] , and mesenchymal stem cells (MSCs) differentiate down an osteogenic lineage and produce markers of bone when injected into infarct tissue in mice 20 . Recent evidence also suggests that matrix stiffening, which is generally regarded as an outcome of disease, may be a contributing factor in disease development.…”

Blockade of TSP1-Dependent TGF-β Activity Reduces Renal Injury and Proteinuria in a Murine Model of Diabetic Nephropathy

“…20 Activation can be achieved by multiple tissue-and disease-specific mechanisms, including modification of the latent complex by reactive oxygen species, proteolysis, integrin binding, cellular contractility, and shear forces, or through binding to thrombospondin 1 (TSP1). [21][22][23][24] We identified the role of TSP1 as a major physiologic activator of latent TGF-␤. 25,26 Activation occurs by a nonproteolytic mechanism through binding of the type 1 repeats of TSP1 to a conserved sequence [leucine serine lysine leucine (LSKL)] in the latency associated peptide (LAP) region of the latent complex: LAP binding to the mature domain is required to confer latency, and the RFK sequence of TSP1 disrupts this interaction.…”