Fibroblasts differentiate into the highly synthetic and contractile myofibroblast phenotype when exposed to substrates with an elastic modulus corresponding to pathologically stiff fibrotic tissue. Cellular responses to changes in substrate stiffness are typically analyzed after hours or days, which does not enable the monitoring of myofibroblast persistence, a hallmark of fibrosis. To determine long-lasting effects on the fibrotic behavior of lung fibroblasts, we followed a novel approach of explanting and repeatedly passaging fibroblasts on silicone substrates with stiffness representing various states of lung health. Fibrotic activity was determined by assaying for myofibroblast proliferation, cell contractility, expression of α-smooth muscle actin, extracellular matrix and active TGFβ1. As predicted, myofibroblast activity was low on healthy soft substrates and increased with increasing substrate stiffness. However, explanting and mechanically priming lung fibroblasts for 3 weeks on pathologically stiff substrates resulted in sustained myofibroblast activity even after the cells were returned to healthy soft cultures for 2 weeks. Such primed cells retained higher fibrotic activity than cells that had been exclusively cultured on soft substrates, and were not statistically different from cells continuously passaged on stiff surfaces. Inversely, priming lung fibroblasts for 3 weeks on soft substrates partially protected from myofibroblast activation after the shift to stiff substrates. Hence, mechano-sensed information relating to physical conditions of the local cellular environment could permanently induce fibrotic behavior of lung fibroblasts. This priming effect has important implications for the progression and persistence of aggressive fibrotic diseases such as idiopathic pulmonary fibrosis.

Myofibroblasts play a key role in the wound-healing process, promoting wound closure and matrix deposition. These cells normally disappear from granulation tissue by apoptosis after wound closure, but under some circumstances, they persist and may contribute to pathological scar formation. Myofibroblast differentiation and apoptosis are both modulated by cytokines, mechanical stress, and, more generally, cell-cell and cell-matrix interactions. Tissue repair allows tissues and organs to recover, at least partially, functional properties that have been lost through trauma or disease. Embryonic skin wounds are repaired without scarring or fibrosis, whereas skin wound repair in adults always leads to scar formation, which may have functional or esthetic consequences, as in the case of hypertrophic scars, for example. Skin wound repair involves a precise remodeling process, particularly in the dermal compartment, during which fibroblasts/myofibroblasts play a central role. This article reviews the origins of myofibroblasts and their role in normal and pathological skin wound healing. This article focuses on traumatic skin wound healing, but largely, the same mechanisms apply in other physiological and pathological settings. Tissue healing in other organs is examined by comparison, as well as the stromal reaction associated with cancer. New approaches to wound/scar therapy are discussed.

Since its first description in wound granulation tissue, the myofibroblast has been recognized to be a key actor in the epithelial-mesenchymal cross-talk that plays a crucial role in many physiological and pathological situations, such as regulation of prostate development, ventilation-perfusion in lung alveoli or organ fibrosis. The presence of myofibroblasts in the stroma reaction to epithelial tumors is well established and many data are accumulating which suggest that the stroma compartment is an active participant in tumor onset and/or evolution. In this review we summarize the evidence in favor of this concept, the main mechanisms that regulate myofibroblast differentiation and function, as well as the biophysical and biochemical factors possibly involved in epithelial-stroma interactions, using liver carcinoma as main model, in view of achieving a better understanding of tumor progression mechanisms and of tools directed toward stroma as eventual therapeutic target.

AimsPathological tissue remodelling by myofibroblast contraction is a hallmark of cardiac fibrosis. Myofibroblasts differentiate from cardiac fibroblasts under the action of transforming growth factor-b1 (TGF-b1), which is secreted into the extracellular matrix as a large latent complex. Integrin-mediated traction forces activate TGF-b1 by inducing a conformational change in the latent complex. The mesenchymal integrins avb5 and avb3 are expressed in the heart, but their role in the activation of TGF-b1 remains elusive. Here, we test whether targeting avb5 and avb3 integrins reduces latent TGF-b1 activation by cardiac fibroblasts with the goal to prevent the formation of a-smooth muscle actin (a-SMA)-expressing cardiac myofibroblasts and their contribution to fibrosis. Methods and resultsUsing a porcine model of induced right ventricular fibrosis and pro-fibrotic culture conditions, we show that integrins avb5 and avb3 are up-regulated in myofibroblast-enriched fibrotic lesions and differentiated cultured human cardiac myofibroblasts. Both integrins autonomously contribute to latent TGF-b1 activation and myofibroblast differentiation, as demonstrated by function-blocking peptides and antibodies. Acute blocking of both integrins leads to significantly reduced TGF-b1 activation by cardiac fibroblast contraction and loss of a-SMA expression, which is restored by adding active TGF-b1. Manipulating integrin protein levels in overexpression and shRNA experiments reveals that both integrins can compensate for each other with respect to TGF-b1 activation and induction of a-SMA expression. ConclusionsIntegrins avb5 and avb3 both control myofibroblast differentiation by activating latent TGF-b1. Pharmacological targeting of mesenchymal integrins is a possible strategy to selectively block TGF-b1 activation by cardiac myofibroblasts and progression of fibrosis in the heart.--

Rationale Inflamed atherosclerotic plaques can be visualized by non-invasive PET-CT imaging with 18FDG, a glucose analog but the underlying mechanisms are poorly understood. Objective Here, we directly investigated the role of Glut1-mediated glucose uptake in ApoE−/− mouse model of atherosclerosis. Methods and Results We first show that the enhanced glycolytic flux in atheromatous plaques of ApoE−/− mice was associated with the enhanced metabolic activity of hematopoietic stem and multi-potential progenitors (HSPCs) and higher Glut1 expression in these cells. Mechanistically, the regulation of Glut1 in ApoE−/− HSPCs was not due to alterations in hypoxia-inducible factor 1α (HIF1α) signaling or the oxygenation status of the bone marrow but was the consequence of the activation of the common β subunit of the granulocyte macrophage colony-stimulating factor/interleukin-3 receptor driving glycolytic substrate utilization by mitochondria. By transplanting BM from WT, Glut1+/−, ApoE−/− and ApoE−/−Glut1+/− mice into hypercholesterolemic ApoE deficient mice, we found that Glut1 deficiency reversed ApoE−/− HSPC proliferation and expansion, which prevented the myelopoiesis and accelerated atherosclerosis of ApoE−/− mice transplanted with ApoE−/− BM and resulted in reduced glucose uptake in the spleen and aortic arch of these mice. Conclusions We identified that Glut1 connects the enhanced glucose uptake in atheromatous plaques of ApoE−/− mice with their myelopoiesis through regulation of HSPC maintenance and myelomonocytic fate and suggest Glut1 as potential drug target for atherosclerosis.