The biology of the myofibroblast

The mechanisms leading to the retraction of the granulation tissue during wound healing have not been fully elucidated to date [reviewed in 1]. Our laboratory several years ago described that fibroblasts present in granulation tissue exhibit several ultrastructural features of smooth muscle cells, including the presence of microfilament bundles with dense bodies scattered within [2]. These cells, called myofibroblasts, have been proposed to play a retractile role in several conditions such as granulation tissue contraction, parenchymal organ retraction, fibromatosis and stromal reaction to epithelial tumors [reviewed in 3]. The coincidence of the presence of myofibroblasts with retractile phenomena has supported this hypothesis. However, direct proof of the presence and activity of contractile elements in myofibroblasts has been possible only after suitable techniques have been developed to localize and quantify cytoskeletal and contractile proteins within the affected organs. For this purpose, the advances in the understanding of cytoskeletal and contractile element morphology and biochemistry in different cells have been of great value [reviewed in 4]. Presently, we know that the cytoskeleton of mesenchymal cells is composed of intermediate filaments which consist of a single protein named vimentin. In muscle cells, however, most intermediate filaments have been shown to contain another related, but not identical, protein which is called desmin. However, vascular smooth muscle cells always express vimentin, and only a proportion of them contains in addition desmin. Moreover, desmin has been increasingly found in a number of nonmuscle mesenchymal cells such as endothelial cells [5,6], podocytes [7] and stromal cells from various locations [7-10]. Another marker of tissue origin is the presence of a specific actin isoform, since the six actin isoform expressing mammals show a tissue specific distribution [4]. In particular, α-smooth muscle actin is present in all smooth muscle cells. Finally, isoforms of myosin heavy and light chains can also be typical of smooth muscle (particularly under normal conditions) and hence assist in identifying cells which are involved in different pathological changes [11]

Fibrosis: recent advances in myofibroblast biology and new therapeutic perspectives

The crucial role of the myofibroblast in wound healing and fibrosis development is well established. This review discusses the mechanisms of myofibroblast action and the new findings that may develop into therapeutic strategies during the next few years

The NH2-terminal peptide of α–smooth muscle actin inhibits force generation by the myofibroblast in vitro and in vivo

Myofibroblasts are specialized fibroblasts responsible for granulation tissue contraction and the soft tissue retractions occurring during fibrocontractive diseases. The marker of fibroblast-myofibroblast modulation is the neo expression of α–smooth muscle actin (α-SMA), the actin isoform typical of vascular smooth muscle cells that has been suggested to play an important role in myofibroblast force generation. Actin isoforms differ slightly in their NH2-terminal sequences; these conserved differences suggest different functions. When the NH2-terminal sequence of α-SMA Ac-EEED is delivered to cultured myofibroblast in the form of a fusion peptide (FP) with a cell penetrating sequence, it inhibits their contractile activity; moreover, upon topical administration in vivo it inhibits the contraction of rat wound granulation tissue. The NH2-terminal peptide of α–skeletal actin has no effect on myofibroblasts, whereas the NH2-terminal peptide of β–cytoplasmic actin abolishes the immunofluorescence staining for this isoform without influencing α-SMA distribution and cell contraction. The FPs represent a new tool to better understand the specific functions of actin isoforms. Our findings support the crucial role of α-SMA in wound contraction. The α-SMA–FP will be useful for the understanding of the mechanisms of connective tissue remodeling; moreover, it furnishes the basis for a cytoskeleton-dependent preventive and/or therapeutic strategy for fibrocontractive pathological situations

Autologous transplantation of culture-born myofibroblasts into intact and injured rabbit ligaments

Purpose: The myofibroblast, a contractile fibroblastic cell expressing α-smooth muscle actin (α-SMA), has been reported to play a role in ligament healing. The aim of this study was to evaluate the feasibility of transplanting culture-derived myofibroblasts in injured rabbit medial collateral ligaments (MCL) and in intact anterior cruciate ligaments (ACL). Methods: Fibroblasts isolated from the iliotibial band were cultured in the presence of transforming growth factor beta-1 (TGF-β1) for fivedays and analysed for α-SMA expression. In a concentration of TGF-β1 ≥ 10ng/ml, the differentiation rate into myofibroblast was 90%. After labelling with PKH26, α-SMA -positive cells were transplanted in intact ACL and in injured MCL of ten rabbits. Results: Survival of PKH-26+ cells was seen in all intact and damaged ligaments one day after injection. The density of PKH-26+ cells had decreased at seven days postinjection in both ligaments. Double-positive PKH-26+/α-SMA+ cells were only observed in injured MCL at sevendays postinjection. Moreover, we found that genetically modified fibroblasts differentiate into myofibroblasts and can be transplanted into ligaments. Conclusions: Our data demonstrate that culture-born myofibroblasts survive and maintain α-SMA expression up to one week after transplantation. This study provides the first insight into the feasibility of transplanted mechanically active cells for ligament reconstructio

Corrigendum to "Cytostatic drugs differentially affect phenotypic features of porcine coronary artery smooth muscle cell populations" [FEBS Lett. 581 (2007) 5847–5851]

n/

Dietary cholesterol withdrawal reduces vascular inflammation and induces coronary plaque stabilization in miniature pigs

Objective: To study the effect of dietary cholesterol withdrawal on size and composition of LDL-hypercholesterolemia-induced coronary plaques in miniature pigs. Methods: Pigs were on normal chow (control group), on a cholesterol-rich diet for 37 weeks (hypercholesterolemic group) or on a cholesterol-rich diet followed by normal chow for 26 weeks (cholesterol withdrawal group). Endothelial function was assessed with quantitative angiography after intracoronary infusion of acetylcholine, plaque load with intra-coronary ultrasound and plaque composition with image analysis of cross-sections. The effect of porcine serum on coronary smooth muscle cell (SMC) function was studied in vitro. Results: Cholesterol-rich diet caused LDL-hypercholesterolemia, increased plasma levels of oxidized LDL (ox-LDL) and C-reactive protein (CRP), and induced endothelial dysfunction and coronary atherosclerosis. Dietary cholesterol withdrawal lowered LDL, ox-LDL and CRP. It restored endothelial function, did not affect plaque size but decreased lipid, ox-LDL and macrophage content. Smooth muscle cells and collagen accumulated within the plaque. Increased smoothelin-to-α-smooth muscle actin ratio indicated a more differentiated SMC phenotype. Cholesterol lowering reduced proliferation and apoptosis. In vitro, hypercholesterolemic serum increased SMC apoptosis and decreased SMC migration compared to non-hypercholesterolemic serum. Conclusions: Cholesterol lowering induced coronary plaque stabilization as evidenced by a decrease in lipids, ox-LDL, macrophages, apoptosis and cell proliferation, and an increase in differentiated SMC and collagen. Increased migration and decreased apoptosis of SMC may contribute to the disappearance of the a-cellular core after lipid lowerin

Modulation of experimental mesangial proliferative nephritis by interferon-γ

Modulation of experimental mesangial proliferative nephritis by interferon-γ. The observation that interferon-γ (IFN-γ) inhibits cell proliferation and collagen synthesis of a variety of cell types in culture has suggested that IFN-γ may be useful in the treatment of fibroproliferative diseases. We administered recombinant IFN-γ subcutaneously (105 U/kg/day for 3 days) to rats, beginning one day after the induction of mesangial proliferative nephritis with anti-Thy 1 antibody. IFN-γ reduced glomerular (primarily mesangial) cell proliferation by 44% at days 2 and 4 compared to vehicle injected control rats with anti-Thy 1 nephritis (that is, proliferating cells that excluded the macrophage marker, ED-1, P < 0.001). Despite the inhibition of mesangial cell proliferation, IFN-γ did not reduce the overall extracellular matrix deposition (by silver stain) or deposition of type IV collagen or laminin (by immunostaining) at 4 or 7 days, and glomerular type IV collagen and laminin mRNA levels were increased (1.4 and 1.7-fold) at 4 days relative to controls. The inability of IFN-γ treatment to reduce mesangial matrix expansion may relate to the fact that IFN-γ treated rats had a twofold increase in glomerular macrophages (that is, ED-1 positive cells, P < 0.001 at 2 and 4 days) with an increase in oxidant producing cells (day 2, P < 0.05) and a 1.6-fold increase in glomerular TGF-β mRNA expression (4 days). This suggests that the effect of IFN-γ to inhibit mesangial cell proliferation in glomerulonephritis may be offset by the ability of IFN-γ to increase glomerular macrophages and TGF-β expression. These data also show that IFN-γ can partly dissociate the mesangial proliferative response from the extracellular matrix expansion in glomerulonephritis

Smooth muscle hyperplasia due to loss of smooth muscle α-actin is driven by activation of focal adhesion kinase, altered p53 localization and increased levels of platelet-derived growth factor receptor-β

Mutations in ACTA2, encoding the smooth muscle cell (SMC)-specific isoform of α-actin (α-SMA), cause thoracic aortic aneurysms and dissections and occlusive vascular diseases, including early onset coronary artery disease and stroke. We have shown that occlusive arterial lesions in patients with heterozygous ACTA2 missense mutations show increased numbers of medial or neointimal SMCs. The contribution of SMC hyperplasia to these vascular diseases and the pathways responsible for linking disruption of α-SMA filaments to hyperplasia are unknown. Here, we show that the loss of Acta2 in mice recapitulates the SMC hyperplasia observed in ACTA2 mutant SMCs and determine the cellular pathways responsible for SMC hyperplasia. Acta2−/− mice showed increased neointimal formation following vascular injury in vivo, and SMCs explanted from these mice demonstrated increased proliferation and migration. Loss of α-SMA induced hyperplasia through focal adhesion (FA) rearrangement, FA kinase activation, re-localization of p53 from the nucleus to the cytoplasm and increased expression and ligand-independent activation of platelet-derived growth factor receptor beta (Pdgfr-β). Disruption of α-SMA in wild-type SMCs also induced similar cellular changes. Imatinib mesylate inhibited Pdgfr-β activation and Acta2−/− SMC proliferation in vitro and neointimal formation with vascular injury in vivo. Loss of α-SMA leads to SMC hyperplasia in vivo and in vitro through a mechanism involving FAK, p53 and Pdgfr-β, supporting the hypothesis that SMC hyperplasia contributes to occlusive lesions in patients with ACTA2 missense mutation