Transforming growth factor-beta induction of alpha-smooth muscle actin is dependent on the deformability of the collagen matrix

Stromal dynamic reciprocity in cancer: intricacies of fibroblastic-ECM interactions

Stromal dynamic reciprocity (SDR) consists of the biophysical and biochemical interplay between connective tissue elements that regulate and maintain organ homeostasis. In epithelial cancers, chronic alterations of SDR result in the once tumor-restrictive stroma evolving into a 'new' tumor-permissive environment. This altered stroma, known as desmoplasia, is initiated and maintained by cancer associated fibroblasts (CAFs) that remodel the extracellular matrix (ECM). Desmoplasia fuels a vicious cycle of stromal dissemination enriching both CAFs and desmoplastic ECM. Targeting specific drivers of desmoplasia, such as CAFs, either enhances or halts tumor growth and progression. These conflicting effects suggest that stromal interactions are not fully understood. This review highlights known fibroblastic-ECM interactions in an effort to encourage therapies that will restore cancer-restrictive stromal cues.

Abrogation of TGF-beta1-induced fibroblast-myofibroblast differentiation by histone deacetylase inhibition

Idiopathic pulmonary fibrosis (IPF) is a devastating disease with no known effective pharmacological therapy. The fibroblastic foci of IPF contain activated myofibroblasts that are the major synthesizers of type I collagen. Transforming growth factor (TGF)-beta1 promotes differentiation of fibroblasts into myofibroblasts in vitro and in vivo. In the current study, we investigated the molecular link between TGF-beta1-mediated myofibroblast differentiation and histone deacetylase (HDAC) activity. Treatment of normal human lung fibroblasts (NHLFs) with the pan-HDAC inhibitor trichostatin A (TSA) inhibited TGF-beta1-mediated alpha-smooth muscle actin (alpha-SMA) and alpha1 type I collagen mRNA induction. TSA also blocked the TGF-beta1-driven contractile response in NHLFs. The inhibition of alpha-SMA expression by TSA was associated with reduced phosphorylation of Akt, and a pharmacological inhibitor of Akt blocked TGF-beta1-mediated alpha-SMA induction in a dose-dependent manner. HDAC4 knockdown was effective in inhibiting TGF-beta1-stimulated alpha-SMA expression as well as the phosphorylation of Akt. Moreover, the inhibitors of protein phosphatase 2A and 1 (PP2A and PP1) rescued the TGF-beta1-mediated alpha-SMA induction from the inhibitory effect of TSA. Together, these data demonstrate that the differentiation of NHLFs to myofibroblasts is HDAC4 dependent and requires phosphorylation of Akt.

A new technique for calculating individual dermal fibroblast contractile forces generated within collagen-GAG scaffolds

Cell-mediated contraction plays a critical role in many physiological and pathological processes, notably organized contraction during wound healing. Implantation of an appropriately formulated (i.e., mean pore size, chemical composition, degradation rate) three-dimensional scaffold into an in vivo wound site effectively blocks the majority of organized wound contraction and results in induced regeneration rather than scar formation. Improved understanding of cell contraction within three-dimensional constructs therefore represents an important area of study in tissue engineering. Studies of cell contraction within three-dimensional constructs typically calculate an average contractile force from the gross deformation of a macroscopic substrate by a large cell population. In this study, cellular solids theory has been applied to conventional column buckling relationships to quantify the magnitude of individual cell contraction events within a three-dimensional, collagen-glycosaminoglycan scaffold. This new technique can be used for studying cell mechanics with a wide variety of porous scaffolds that resemble low-density, open-cell foams. It extends previous methods for analyzing cell buckling of two-dimensional substrates to three-dimensional constructs. From data available in the literature, the mean contractile force (Fc) generated by individual dermal fibroblasts within the collagen-glycosaminoglycan scaffold was calculated to range between 11 and 41 nN (Fc=26+/-13 nN, mean+/-SD), with an upper bound of cell contractility estimated at 450 nN.

Phenotypic differences between dermal fibroblasts from different body sites determine their responses to tension and TGFbeta1

BACKGROUND

Wounds in the nonglabrous skin of keloid-prone individuals tend to cause large disordered accumulations of collagen which extend beyond the original margins of the wound. In addition to abnormalities in keloid fibroblasts, comparison of dermal fibroblasts derived from nonwounded glabrous or nonglabrous skin revealed differences that may account for the observed location of keloids.

METHODS

Fibroblast apoptosis and the cellular content of alpha-smooth-muscle actin, TGFbeta1 receptorII and ED-A fibronectin were estimated by FACS analysis. The effects of TGFbeta1 and serum were examined.

RESULTS

In monolayer cultures non-glabrous fibroblasts were slower growing, had higher granularity and accumulated more alpha-smooth-muscle actin than fibroblasts from glabrous tissues. Keloid fibroblasts had the highest level of alpha-smooth-muscle actin in parallel with their expression level of ED-A fibronectin. TGFbeta1 positively regulated alpha-smooth-muscle actin expression in all fibroblast cultures, although its effects on apoptosis in fibroblasts from glabrous and non-glabrous tissues were found to differ. The presence of collagen I in the ECM resulted in reduction of alpha-smooth-muscle actin. A considerable percentage of the apoptotic fibroblasts in attached gels were alpha-smooth-muscle actin positive. The extent of apoptosis correlated positively with increased cell and matrix relaxation. TGFbeta1 was unable to overcome this apoptotic effect of matrix relaxation.

CONCLUSION

The presence of myofibroblasts and the apoptosis level can be regulated by both TGFbeta1 and by the extracellular matrix. However, reduction of tension in the matrix is the critical determinant. This predicts that the tension in the wound bed determines the type of scar at different body sites.

Myofibroblast phenotype and apoptosis in keloid and palmar fibroblasts in vitro

Keloid formation is a wound healing response, which fails to resolve and leads to formation of a raised collagen mass extending beyond the original wound margins. Keloids are typically excluded from palms and soles. Therefore we compared keloid and palmar fibroblasts in vitro using fibroblasts from nonaffected individuals as controls. Collagen I, alpha-smooth muscle actin and thrombospondin-1 were found at higher levels in keloid than in palmar fibroblasts. These differences were ameliorated by addition of TGFbeta1. The potential for resolution of the wound healing response was estimated analyzing apoptosis during serum starvation. Annexin V and TUNEL assays showed that palmar fibroblasts underwent faster apoptosis, than did the keloid fibroblasts, and started detaching. Addition of TGFbeta1 counteracted this effect. The weak expression of the myofibroblast phenotype and the advanced apoptosis of palmar fibroblasts suggest mechanisms for the exclusion of keloids from palmar sites.