Transforming growth factor-beta 1 induces alpha-smooth muscle actin expression in granulation tissue myofibroblasts and in quiescent and growing cultured fibroblasts

Transfer of tumor necrosis factor-alpha to rat lung induces severe pulmonary inflammation and patchy interstitial fibrogenesis with induction of transforming growth factor-beta1 and myofibroblasts

Tumor necrosis factor-alpha is up-regulated in a variety of different human immune-inflammatory and fibrotic pulmonary pathologies. However, its precise role in these pathologies and, in particular, the mechanism(s) by which it may induce fibrogenesis are not yet elucidated. Using a replication-deficient adenovirus to transfer the cDNA of tumor necrosis factor-alpha to rat lung, we have been able to study the effect of transient but prolonged (7 to 10 days) overexpression of tumor necrosis factor-alpha in normal adult pulmonary tissue. We have demonstrated that local overexpression resulted in severe pulmonary inflammation with significant increases in neutrophils, macrophages, and lymphocytes and, to a lesser extent, eosinophils, with a peak at day 7. By day 14, the inflammatory cell accumulation had declined, and fibrogenesis became evident, with fibroblast accumulation and deposition of extracellular matrix proteins. Fibrotic changes were patchy but persisted to beyond day 64. To elucidate the mechanism underlying this fibrogenesis, we examined bronchoalveolar fluids for the presence of the fibrogenic cytokine transforming growth factor-beta1 and tissues for induction of alpha-smooth muscle actin-rich myofibroblasts. Transforming growth factor-beta1 was transiently elevated from day 7 (peak at day 14) immediately preceding the onset of fibrogenesis. Furthermore, there was a striking accumulation of myofibroblasts from day 7, with the most extensive and intense immunostaining at day 14, ie, coincident with the up-regulation of transforming growth factor-beta1 and onset of fibrogenesis. Thus, we have provided a model of tumor necrosis factor-alpha-mediated pulmonary inflammation and fibrosis in normal adult lung, and we suggest that the fibrogenesis may be mediated by the secondary up-regulation of transforming growth factor-beta1 and induction of pulmonary myofibroblasts.

Stem cell factor induction is associated with mast cell accumulation after canine myocardial ischemia and reperfusion

BACKGROUND

Myocardial infarction is associated with an intense inflammatory reaction leading to healing and scar formation. Because mast cells are a significant source of fibrogenic factors, we investigated mast cell accumulation and regulation of stem cell factor (SCF), a potent growth and tactic factor for mast cells, in the healing myocardium.

METHODS AND RESULTS

Using a canine model of myocardial ischemia and reperfusion, we demonstrated a striking increase of mast cell numbers during the healing phase of a myocardial infarction. Mast cell numbers started increasing after 72 hours of reperfusion, showing maximum accumulation in areas of collagen deposition (12.0+/-2.6-fold increase; P<0.01) and proliferating cell nuclear antigen (PCNA) expression. The majority of proliferating cells were identified as alpha-smooth muscle actin-positive myofibroblasts or factor VIII-positive endothelial cells. Mast cells did not appear to proliferate. Using a nuclease protection assay, we demonstrated induction of SCF mRNA within 72 hours of reperfusion. Immunohistochemical studies demonstrated that a subset of macrophages was the source of SCF immunoreactivity in the infarcted myocardium. SCF protein was not found in endothelial cells and myofibroblasts. Intravascular tryptase-positive, FITC-avidin-positive, CD11b-negative mast cell precursors were noted in the area of healing and in the cardiac lymph after 48 to 72 hours of reperfusion.

CONCLUSIONS

Mast cells increase in number in areas of collagen deposition and PCNA expression after myocardial ischemia. The data provide evidence of mast cell precursor infiltration into the areas of cellular injury. SCF is induced in a subset of macrophages infiltrating the healing myocardium. We suggest an important role for SCF in promoting chemotaxis and growth of mast cell precursors in the healing heart.

The fibronectin domain ED-A is crucial for myofibroblastic phenotype induction by transforming growth factor-beta1

Transforming growth factor-beta1 (TGFbeta1), a major promoter of myofibroblast differentiation, induces alpha-smooth muscle (sn) actin, modulates the expression of adhesive receptors, and enhances the synthesis of extracellular matrix (ECM) molecules including ED-A fibronectin (FN), an isoform de novo expressed during wound healing and fibrotic changes. We report here that ED-A FN deposition precedes alpha-SM actin expression by fibroblasts during granulation tissue evolution in vivo and after TGFbeta1 stimulation in vitro. Moreover, there is a correlation between in vitro expression of alpha-SM actin and ED-A FN in different fibroblastic populations. Seeding fibroblasts on ED-A FN does not elicit per se alpha-SM actin expression; however, incubation of fibroblasts with the anti-ED-A monoclonal antibody IST-9 specifically blocks the TGFbeta1-triggered enhancement of alpha-SM actin and collagen type I, but not that of plasminogen activator inhibitor-1 mRNA. Interestingly, the same inhibiting action is exerted by the soluble recombinant domain ED-A, but neither of these inhibitory agents alter FN matrix assembly. Our findings indicate that ED-A-containing polymerized FN is necessary for the induction of the myofibroblastic phenotype by TGFbeta1 and identify a hitherto unknown mechanism of cytokine-determined gene stimulation based on the generation of an ECM-derived permissive outside in signaling, under the control of the cytokine itself.

Physiology and healing dynamics of chronic cutaneous wounds

In the last few decades, a great deal of progress has been made in understanding the cellular and biochemical interplay that comprises the normal wound healing response. This response is a complex process involving intricate interactions among a variety of different cell types, structural proteins, growth factors, and proteinases. The normal wound repair process consists of three phases--inflammation, proliferation, and remodeling--that occur in a predictable sequence and comprise a series of cellular and biochemical events. A review of the biochemical and physiologic processes that regulate wound healing and the cascade of cellular events that gives rise to the healing process is presented here.

Study on myofibroblast differentiation in the stromal cells of Wharton's jelly: expression and localization of alpha-smooth muscle actin

To confirm the characteristics of the stromal cells of Wharton's jelly, we investigated the morphological changes in these cells during each trimester of pregnancy. We evaluated the cytoskeletal features of these cells by examining immunohistochemically the localization of one of the contractile proteins, alpha-smooth muscle actin (ASMA). After the second trimester, the stromal cells of Wharton's jelly were stained with ASMA antibody, exhibited the ultrastructural characteristics of the myofibroblasts, and began to express numerous microfilaments in the cytoplasm. Postembedding immunogold labeling detected immunoreactivity for ASMA on these microfilaments. The finding indicated that the stromal cells of Wharton's jelly undergo a time-dependent maturation involving the differentiation of myofibroblasts during the last 6 months of pregnancy. These cells possess a contractile function that may help to protect the umbilical vessels from compression, considering that ASMA was detected in the microfilamentous bundles.

Immunohistochemical study of proliferating mesenchymal spindle cells in heterogenous soft tissue lesions

Proliferation of mesenchymal spindle cells is a main event in a variety of lesions with similar morphological features but widely divergent biological behaviour. In order to identify criteria for precise histological diagnosis, 60 human soft tissue lesions, divided into 40 cases of fibroblastic cell proliferation, 10 smooth muscle cell tumours and 10 nerve sheath cell tumours, were examined for the immunohistochemical profile of the main lesional cell in addition to other histological features. The three groups could be differentiated by determining the lineage of the constituent spindle cell on the pattern of expression of vimentin, alpha-smooth muscle actin (ASMA) and macrophage antigen CD68 (MA-CD68). Smooth muscle cells expressed ASMA and vimentin but not MA-CD68, while nerve sheath cells were negative for ASMA but positive for vimentin and MA-CD68. The fibroblastic cell lesions as a group were easily differentiated on the basis of positive reactivity for all three markers but individual lesions could only be distinguished by additional assessment of histological features. Because of consistent co-expression of ASMA, vimentin and MA-CD68 in the spindle mesenchymal cell present in all varieties of lesions in this heterogeneous group, we suggest that this proliferating "fibroblastic" cell is phenotypically a fibromyohistiocyte.

Transforming growth factor beta1 involvement in the conversion of fibroblasts to smooth muscle cells in the rabbit bladder serosa

In an attempt to identify the growth factors or cytokines involved in the serosal thickening that occurs in rabbit bladder subjected to partial outflow obstruction, the following growth factors--transforming growth factor beta1, platelet-derived growth factor, epidermal growth factor, granulocyte colony-stimulating factor and granulocyte-monocyte colony-stimulating factor--were delivered separately onto the serosal surface of the intact bladder via osmotic minipumps. The proliferative/differentiative cellular response of the rabbit bladder wall was evaluated by bromodeoxyuridine incorporation and immunofluorescence staining with a panel of monoclonal antibodies to cytoskeletal proteins (desmin, vimentin, keratins 8 and 18 and non-muscle myosin) and to smooth muscle (alpha-actin, myosin and SM22) proteins. Administration of the transforming growth factor, but not of the other growth factors/cytokines, was effective in inducing serosal thickening. Accumulating cells in this tissue were identified as myofibroblasts, i.e. cells showing a mixed fibroblast-smooth muscle cell differentiation profile. The phenotypic pattern of myofibroblasts changed in a time-dependent manner: 21 days after the growth factor delivery, small bundles of smooth muscle cells were found admixed with myofibroblasts, as occurs in the obstructed bladder. These 'ectopic' muscle structures displayed a variable proliferating activity and expressed an immature smooth muscle cell phenotype. The complete cellular conversion to smooth muscle cells was not achieved if transforming growth factor beta1 was delivered to fibroblasts of subcutaneous tissue. These findings suggest a tissue-specific role for this growth factor in the cellular conversion from myofibroblast to smooth muscle cells.

Retroviral-mediated marker gene transfer in hematopoiesis-supportive marrow stromal cells

A Moloney-derived retrovirus containing both LacZ and NeoR genes (G1BgSVNa from Genetic Therapy, Inc.), was used to transduce human and murine bone marrow stromal cells. Different kinds of stromal cells that were able to support hematopoiesis were transduced by incubation for 24 h in the presence of virus-containing supernatant. Semiconfluent layers of MRC-5 (human, myofibroblastic, fetal, pulmonary) and MS-5 (murine, myofibroblastic, medullary) cells were successfully transduced after one 24-h incubation, as demonstrated by G418 resistance and Escherichia coli beta-galactosidase staining. In contrast, human stromal cells, purified from primary confluent layers grown for 3-4 weeks, could not be transduced. However, stromal cells generated after 10-12 days in culture from Stro-1+ and 1B10+ stromal precursors were successfully transduced in the presence of basic fibroblast growth factor. Transduced stromal cells maintained a myofibroblastic phenotype, although with a decreased number of alpha-SM actin-positive microfilaments in MS-5 cells. The ability to support the generation of stroma-adherent colony-forming cells from cocultured cord blood CD34+ cells after 4 weeks in culture was similar before and after transduction and G418 selection. In conclusion, human primary stromal precursors can be efficiently transduced, and the stromal cell phenotype and function are not significantly altered after retroviral-mediated transfer of marker genes.

PDGF, TGF-beta, and heterotypic cell-cell interactions mediate endothelial cell-induced recruitment of 10T1/2 cells and their differentiation to a smooth muscle fate

We aimed to determine if and how endothelial cells (EC) recruit precursors of smooth muscle cells and pericytes and induce their differentiation during vessel formation. Multipotent embryonic 10T1/2 cells were used as presumptive mural cell precursors. In an under-agarose coculture, EC induced migration of 10T1/2 cells via platelet-derived growth factor BB. 10T1/2 cells in coculture with EC changed from polygonal to spindle-shaped, reminiscent of smooth muscle cells in culture. Immunohistochemical and Western blot analyses were used to examine the expression of smooth muscle (SM)-specific markers in 10T1/2 cells cultured in the absence and presence of EC. SM-myosin, SM22alpha, and calponin proteins were undetectable in 10T1/2 cells cultured alone; however, expression of all three SM-specific proteins was significantly induced in 10T1/2 cells cocultured with EC. Treatment of 10T1/2 cells with TGF-beta induced phenotypic changes and changes in SM markers similar to those seen in the cocultures. Neutralization of TGF-beta in the cocultures blocked expression of the SM markers and the shape change. To assess the ability of 10T1/2 cells to contribute to the developing vessel wall in vivo, prelabeled 10T1/2 cells were grown in a collagen matrix and implanted subcutaneously into mice. The fluorescently marked cells became incorporated into the medial layer of developing vessels where they expressed SM markers. These in vitro and in vivo observations shed light on the cell-cell interactions that occur during vessel development, as well as in pathologies in which developmental processes are recapitulated.

Basic FGF, EGF, and PDGF modify TGFbeta-induction of smooth muscle cell phenotype in human prostatic stromal cells

BACKGROUND

We investigated the ability of a variety of growth factors to regulate the differentiation of prostatic fibroblasts into smooth muscle cells.

METHODS

Smooth muscle actin levels were monitored by immunoblot analysis and immunocytochemistry. Proliferation was measured in clonal growth assays and by cell counts.

RESULTS

We determined that TGFbeta inhibited proliferation and induced smooth muscle differentiation of stromal cells derived from prostatic adenocarcinomas, as we previously reported for cells derived from the normal peripheral zone. Basic FGF, EGF, TGFalpha, and PDGF, but not IGF, retinoic acid, 1,25-dihydroxyvitamin D3, or androgen, attenuated induction of differentiation by TGFbeta, by a mechanism apparently unrelated to proliferation.

CONCLUSIONS

Regulation of growth and differentiation occurs equivalently in prostatic stromal cells derived from adenocarcinomas and normal peripheral zone. TGFbeta is a potent inducer of the smooth muscle phenotype. Basic FGF, EGF and/or TGFalpha, and PDGF attenuate TGFbeta's activity, and promote a fibroblastic phenotype. Our studies provide an in vitro model system in which fibroblastic or smooth muscle cells can be promoted, maintained, and investigated in a defined manner. The results suggest that the ratio of fibroblasts to smooth muscle cells in the stroma reflects the relative levels of growth factors, which may be altered in diseased states.

TGF-beta in glomerular disease

Transforming growth factor-beta (TGF-beta) is an important cytokine in glomerular disease. Its major role may be to mediate extracellular matrix deposition, by both increasing the synthesis of matrix components and by reducing their degradation. Strong evidence supports the functional role for TGF-beta in mesangial matrix expansion. However, TGF-beta may also have other important functions in the glomerulus, including the regulation of cell proliferation, hypertrophy, and survival (apoptosis), as well as modulation of the local and systemic immune response.

Parathyroid hormone-related protein expression and secretion in a skin organotypic culture system

Parathyroid hormone-related protein (PTHrP), an important factor in the pathogenesis of humoral hypercalcemia of malignancy, is produced by many normal tissues, including the epidermis, where it is thought to play a role in the regulation of keratinocyte growth and differentiation. Most in vitro studies of normal keratinocytes use monolayer cell cultures, which have limitations, including the inability to reproduce the stratified structure of the epidermis. The objective of this study was to investigate PTHrP production and secretion, and mRNA expression in skin organotypic cultures. The cultures consisted of an artificial dermis with differentiating keratinocytes grown at the air-liquid interface. Immunohistochemical assessment of cytokeratins 14 and 10/13, involucrin, and proliferative cell nuclear antigen (PCNA) demonstrated that keratinocytes differentiated in a manner similar to keratinocytes in normal epidermis. PTHrP expression was demonstrated in all viable layers of the epidermis, as well as in some fibroblasts of the collagen lattice by immunohistochemistry and in situ hybridization. Since most fibroblasts expressed alpha-smooth muscle actin, these cells were interpreted to be consistent with myofibroblasts. PTHrP expression by myofibroblasts suggests a possible role for PTHrP in the regulation of contractibility of these cells. PTHrP was also detected in conditioned media for 50 days. In conclusion, because of its superior tissue morphology and ability to induce organized keratinocyte differentiation, this culture system will be an excellent model to study the role of PTHrP in pathologic and physiologic processes involving the epidermis in vitro.

Expression of connective tissue growth factor in human renal fibrosis

Chronic renal failure may occur in etiologically diverse renal diseases and can be caused by hemodynamic, immunologic and metabolic factors. Initial damage may evoke irreversible scarring, which involves production of a number of proinflammatory and fibrogenic cytokines, including platelet-derived growth factor (PDGF) and transforming growth factor beta (TGF-beta). Connective tissue growth factor (CTGF), a cytokine of the family of growth regulators comprising sef10, cyr61, CTGF and nov, has recently been described in association with scleroderma and other scarring conditions. We investigated CTGF mRNA expression in 65 human renal biopsy specimens of various renal diseases by in situ hybridization. In control human kidney CTFG mRNA was mainly expressed in visceral epithelial cells, parietal epithelial cells, and some interstitial cells. Connective tissue growth factor was strongly up-regulated in the extracapillary and severe mesangial proliferative lesions of crescentic glomerulonephritis, IgA nephropathy, focal and segmental glomerulosclerosis and diabetic nephropathy. An increase in the number of cells expressing CTGF mRNA was observed at sites of chronic tubulointerstitial damage, which correlated with the degree of damage. in the tubulointerstitial area the majority of the CTGF mRNA positive cells coexpressed alpha-smooth muscle actin, and were negative for macrophage markers. Our results indicate that CTGF may be a common growth factor involved in renal fibrosis.

Differential response of activated versus non-activated renal fibroblasts to tubular epithelial cells: a model of initiation and progression of fibrosis?

BACKGROUND/AIMS

The mechanisms of initiation and maintenance of renal fibrosis remain obscure, but one hypothesis highlights the importance of tubular epithelial cell-interstitial fibroblast interactions and suggests that tubular injury may be a precipitating factor. The aims of the study were to examine the effects of factors of proximal tubular origin on renal fibroblasts expressing different levels of smooth muscle actin (SMA; a putative marker of fibroblast activation) and to examine the modulation of SMA by extracellular matrix (ECM) proteins and transforming growth factor beta 1 (TGF-beta 1), a major profibrotic cytokine.

METHODS

Primary cultures of rat cortical fibroblasts (CF) and the rat kidney fibroblast cell line NRK-49F were (1) cultured on different ECM proteins; (2) treated with medium conditioned by rat proximal tubular epithelial cells (PTE), and (3) treated with TGF-beta 1. SMA protein expression was examined by immunocytochemistry, while expression of MMP-2, MMP-3, TIMP-1, and collagen I mRNA was determined by Northern blot analysis or reverse-transcriptase polymerase chain reaction.

RESULTS

In cells with low basal levels of SMA (CF), serum was the most potent inducer of increased SMA expression, although ECM proteins also modulated expression. With high basal levels of SMA expression (NRK), ECM proteins alone had little or no effect, but acted synergistically with serum to stimulate expression. In CF, PTE-conditioned medium (CM) had no effect on SMA and TIMP mRNA levels, but suppressed expression of MMP mRNAs. In NRK-49F, PTE-CM stimulated SMA and TIMP-1 mRNA levels, but had no effect on MMP mRNA levels. Although TGF-beta 1 modulated some cellular responses in NRK-49F, neutralizing antibody studies showed it was not the main mediator of the PTE-CM-induced effects.

CONCLUSIONS

These data suggest (1) that in renal fibroblasts SMA expression can be modulated by both serum and ECM proteins and (2) that PTE induce a fibrogenic phenotype in both non-activated (low SMA) and activated (high SMA) fibroblasts via different mechanisms.

Immunolocalization of prolyl 4-hydroxylase subunits, alpha-smooth muscle actin, and extracellular matrix components in human lens capsules with lens implants

Lens capsules become fibrotic after the extraction of a cataract. To understand this phenomenon, we evaluated the immunolocalization of prolyl 4-hydroxylase (an enzyme involved in procollagen hydroxylation), and extracellular matrix components and cytoskeletal components in a normal human lens capsule and in others with intraocular lenses. Lens capsules containing intraocular lenses were removed from a patient with proliferative vitreoretinopathy and three with proliferative diabetic retinopathy during vitreous surgery. Two circular sections of the anterior capsules with lens epithelial cells were obtained by anterior capsulotomy during cataract surgery. In addition, a lens capsular bag was obtained immediately after phacoemulsification. The lens capsules were processed for light microscopic immunohistochemical detection of the alpha and beta subunits of prolyl 4-hydroxylase, extracellular matrix components (including collagen types, laminin and cellular fibronectin) or cytoskeletal components (such as cytokeratin, vimentin and alpha-smooth muscle actin). Monolayer lens epithelial cells were seen on the inner surface of the normal anterior capsules. Each intraocular lens was found to be fixed in the capsular bag. Light microscopic immunohistochemistry showed that these proliferating cells expressed vimentin and alpha-smooth muscle actin; in contrast, quiescent lens epithelial cells did not stain for alpha-smooth muscle actin. Marked immunostaining for subunits of prolyl 4-hydroxylase was detected in lens epithelial cells proliferating on the capsules, while no or only faint prolyl 4-hydroxylase immunoreactivity was detected in quiescent lens epithelial cells immediately after phacoemulsification. Collagen types I, III and VI and cellular fibronectin were observed diffusely in accumulated connective tissue on a capsule with an intraocular lens. Type IV collagen immunoreactivity was seen both in the capsules and in the connective tissue accumulation on the capsules. Collagen V and laminin were detected in association with cellular proliferation. Collagen VII and VIII and laminin 5 were not seen. We concluded that during wound healing of the lens capsule after cataract extraction, the lens epithelial cells that proliferate on the inner surface of the capsule transform it into a myofibroblastic phenotype, expressing prolyl 4-hydroxylase and alpha-smooth muscle actin. These proliferating cells are involved in the production of collagen on the lens capsule. This results in a postoperative fibrotic process and contraction of the lens capsule.

Enhanced expression of transforming growth factor-beta type I and type II receptors in wound granulation tissue and hypertrophic scar

In the present study we have analyzed and compared, by immunohistochemistry and in situ hybridization, the expression pattern of the R4/ALK5 transforming growth factor (TGF)-beta type I receptor (RI) and the TGF-beta type II receptor (RII) in normal human skin, in wounded skin at various stages during the transition of wound granulation tissue to scar, and in long-persisting post-burn hypertrophic scars. In normal human skin, expression of RI and RII was clearly visible in the epidermis, in epidermal appendages, and in vascular cells, although only a small number of dermal fibroblasts revealed detectable levels of TGF-beta receptor expression. In contrast, granulation tissue fibroblasts showed strong expression of both TGF-beta receptor types, although in normal-healing excisional wounds their density decreased during granulation tissue remodeling. However, in post-burn hypertrophic scars, RI- and RII-overexpressing fibroblasts were found in high densities up to 20 months after injury. From these findings we suggest that the repair process of deep wounds involves the transformation of a subset of fibroblastic cells toward an increased TGF-beta responsiveness and a transient accumulation of these cells at the wound site. In addition, our study provides evidence that excessive scarring is associated with a failure to eliminate TGF-beta receptor-overexpressing fibroblasts during granulation tissue remodeling, which leads to a persistent autocrine, positive feedback loop that results in over-production of matrix proteins and subsequent fibrosis.

Local angiotensin II and myocardial fibrosis

Tissue repair appears in the infarcted heart at both infarcted and noninfarcted myocardium. Experimental evidence gathered to date indicates that myoFb are the predominant cell responsible for collagen formation at sites of repair in the rat heart and related structures. These phenotypically transformed fibroblast-like cells are not normal residents of ventricular tissue. They appear on day 4 at sites of injury and remain abundant for weeks therefore. MyoFb express type I collagen mRNA and ACE and AT1 receptors. ACE inhibitors or AT1 receptor antagonists attenuate collagen accumulation in both infarcted and noninfarcted myocardium. These findings suggest locally generated AngII may have an autocrine function in regulating myoFb collagen turnover.

Modulated response to cytokines of human wound healing myofibroblasts compared to dermal fibroblasts

Myofibroblasts play an important role in normal wound healing. They are present transiently during tissue repair. Their differentiation from fibroblasts and their role in granulation tissues are most likely to be modulated by cytokines. As these cells are derived from normal fibroblasts, their responses to cytokines are assumed to be similar. Until now, however, the difficulties in obtaining and maintaining normal human wound healing myofibroblasts in vitro have hampered comparison. The present study was designed to determine the effect of TGF-beta 1 and IFN-gamma, two cytokines known to modulate fibroblast morphology, on wound healing myofibroblasts and to compare it to fibroblasts. Morphological and phenotypic changes were followed by light and electron microscopy (stress fibers) and immunofluorescence cytochemistry (alpha-SM actin). Functional parameters such as the capacity to synthesize collagen and collagen gel contraction were studied. Both cytokines induced a strong modification of growth rate and phenotypic and morphological parameters in fibroblasts whereas collagen synthesis was slightly changed. Furthermore, TGF-beta 1 increased contractile capacity of fibroblasts whereas IFN-gamma greatly decreased it. In myofibroblasts, TGF-beta 1 and IFN-gamma did not induce any variation of morphology or growth rate. Interestingly, a strong modulation of functional parameters was observed: collagen synthesis was highly modified and, as for fibroblasts, the contractile capacity was altered. However, inhibition of contraction by IFN-gamma was irreversible in myofibroblasts but not in fibroblasts. These results suggest that fibroblastic cells show modulated responses to cytokines according to their stage of differentiation during wound healing.

Expression of interleukin-10 by in vitro and in vivo activated hepatic stellate cells

Activated hepatic stellate cells (HSC) participate in matrix remodeling and deposition in liver fibrosis. The present study demonstrates that interleukin (IL)-10 is expressed by HSC upon activation in vitro or in vivo and that autocrine effects of this cytokine include inhibition of collagen production. Culture activation of HSC caused a distinct increase in IL-10 mRNA level compared with freshly isolated quiescent HSC. Treatment of cultured HSC with tumor necrosis factor-alpha, transforming growth factor-beta, or lipopolysaccharide further increased IL-10 mRNA by 2-fold and resulted in the release of IL-10 protein into the medium. HSC isolated from rats after bile duct ligation (BDL) showed prominent increases in IL-10 mRNA (x 100) and protein (x 30) levels at 7 days after BDL, but such induction disappeared in advanced liver fibrosis (19 days after BDL). IL-10 expression correlated positively with mRNA expression of interstitial collagenase and inversely with that of alpha1(I) collagen. Addition of anti-IL-10 IgG to cultured HSC caused enhanced collagen production under a basal or stimulated condition with TGF-beta, tumor necrosis factor-alpha, or lipopolysaccharide. These effects were associated with increased alpha1(I) collagen mRNA and reciprocally reduced collagenase mRNA levels. Co-transfection of HSC with an IL-10 expression vector and collagen reporter genes showed a 40% inhibition of alpha1(I) collagen promoter activity. These results demonstrate that activation of HSC causes enhanced autocrine expression of IL-10 which possesses a negative autoregulatory effect on HSC collagen production mediated at least in part by alpha1(I) collagen transcriptional inhibition and stimulation of collagenase expression. These findings, along with the demonstrated early induction of HSC IL-10 expression and its late disappearance during biliary liver fibrosis, suggest its in vivo role in matrix remodeling and a possibility that failure for HSC to sustain IL-10 expression underlies pathologic progression to liver cirrhosis.

The molecular basis of keloid and hypertrophic scar formation

Excess scar formation secondary to traumatic or surgical injuries can have devastating consequences, ranging from body disfigurement to organ dysfunction. Hypertrophic scars and keloids are skin fibrotic conditions that can be caused by minor insults to skin, such as acne or ear piercing, or by severe injuries such as burns. Differences between keloids, hypertrophic scars and normal scars include distinct scar appearance, histologic morphology and cellular function in response to growth factors. Recent advances in our understanding of the wound healing process reveal possible causes for hypertrophic scars and keloids. This information might assist in the development of efficacious treatment for hypertrophic scar and keloid formation.

Cellular retinol-binding protein-1 is transiently expressed in granulation tissue fibroblasts and differentially expressed in fibroblasts cultured from different organs

We have reported that cellular retinol-binding protein-1 (CRBP-1) is transiently expressed by arterial smooth muscle cells during experimental intimal repair (P. Neuville, A. Geinoz, G. Benzonana, M. Redard, F. Gabbiani, P. Ropraz, G. Gabbiani: Am J Pathol 1997, 150:509-521). We have examined here the expression of CRBP-1 during wound healing after a full-thickness rat skin wound. CRBP-1 was transiently expressed by a significant proportion of fibroblastic cells including myofibroblasts. Expression started 4 days after wounding, reached a maximum at 12 days, and persisted up to 30 days when a scar was formed. After wound closure, most CRBP-1-containing fibroblastic cells underwent apoptosis. We have further investigated CRBP-1 expression in rat fibroblasts cultured from different organs. CRBP-1 was abundant in lung and heart fibroblasts and was detected in decreasing amounts in muscle, tendon, subcutaneous tissue, and granulation tissue fibroblasts. Dermis fibroblasts contained no detectable levels of CRBP-1. All-trans retinoic acid and transforming growth factor-beta1 inhibited cell proliferation and increased CRBP-1 expression in fibroblastic populations except dermis fibroblasts. We demonstrate that during granulation tissue formation a subpopulation of fibroblastic cells express CRBP-1 de novo. We also demonstrate that CRBP-1 expression by fibroblasts is regulated in vitro by retinoic acid and transforming growth factor-beta1. Our results suggest that CRBP-1 and possibly retinoic acid play a role in the evolution of granulation tissue.

Angiotensin II-induced stimulation of smooth muscle alpha-actin expression by serum response factor and the homeodomain transcription factor MHox

The objective of the present study was to examine the molecular mechanisms whereby angiotensin II (Ang II) stimulates smooth muscle (SM) alpha-actin expression in rat aortic smooth muscle cells (SMCs). Nuclear run-on analysis and transfection studies indicated that the effects of Ang II on SM alpha-actin were mediated at least in part at the transcriptional level. Transfection of various rat SM alpha-actin promoter/chloramphenicol acetyltransferase (CAT) constructs into SMCs demonstrated that the first 155 bp of the SM alpha-actin promoter was sufficient to confer maximal Ang II responsiveness, conferring an approximately 4-fold increase in reporter activities in these SMCs compared with vehicle-treated SMCs. Mutation of either of two highly conserved CArG elements, designated A (-62) and B (-112), completely abolished Ang II-induced increases in reporter activity, whereas mutation of a homeodomain-like binding sequence at -145 (ATTA) reduced reporter activity by half. Results of EMSAs showed that nuclear extracts from Ang II-treated SMCs exhibited enhanced binding activity of serum response factor (SRF) to the CArG elements and of a homeodomain factor, MHox, to the ATTA element. Northern analyses showed that Ang II also stimulated marked increases in MHox mRNA levels. Western analyses demonstrated that Ang II-induced increases in SRF binding were not due to increased SRF protein expression. Recombinant MHox markedly enhanced binding activity of SRF in EMSAs. Finally, MHox overexpression transactivated a SM alpha-actin promoter/CAT reporter construct by approximately 3.5-fold in transient cotransfection studies. These results provide evidence for involvement of a homeodomain transcription factor, MHox, in Ang II-mediated stimulation of SM alpha-actin via a CArG/SRF-dependent mechanism.

Expression of fibronectin and tenascin-C mRNA by myofibroblasts, vascular cells and epithelial cells in human colon adenomas and carcinomas

To understand the mechanisms of tissue remodeling during cancer progression, it is important to know the type of cells that actively express extracellular matrix (ECM) proteins. Twenty-nine adenocarcinomas, 5 adenomas and non-neoplastic mucosa samples were therefore investigated to determine their fibronectin (FN) and tenascin-C (TN-C) expression using in situ hybridization (ISH) and immunohistochemical staining. In the non-neoplastic mucosa, no mRNA signals were found. Two of the adenomas demonstrated positive signals in peri-cryptal cells and the vessels. In the cancers, TN-C and FN mRNAs were found in 86% and 96% of the total cases, respectively. The signals were mainly detected in myofibroblasts, labeled with alpha-smooth muscle actin, in the cancer stroma. TN-C mRNA-positive cells were often observed in localized areas, such as in cancer stroma associated with invading edges and/or in host tissues surrounding the invading cancer front, but rarely in the center of the tumors. FN mRNA-positive cells were more widely spread throughout the cancer stroma, although they were also frequently observed at invading edges. Vascular cells in cancer tissues were also labeled. In 10 specimens, cancer cells themselves expressed FN and/or TN-C mRNA. Comparison with histo-pathological findings revealed positive relationships between the degree of mRNA expression of FN and TN-C and the depth of invasion as well as the frequency of metastasis to lymph nodes. The expression of FN and TN-C by myofibroblasts, vascular cells and cancer cells could be important for the remodeling process of neoplastic tissues during cancer development and progression.

Expression of alpha-smooth muscle actin, TGF-beta 1 and TGF-beta type II receptor during connective tissue contraction

Closure of rat mesenteric perforation is considered to occur by connective tissue contraction, a process that has been shown to be stimulated by transforming growth factor-beta 1. In the present study, we assessed the expression of alpha-smooth muscle actin during closure by quantitative-reverse transcription-polymerase chain reaction and in situ hybridization. The expression of transforming growth factor-beta 1 and transforming growth factor-beta type II receptor was also estimated in mesenteric membranes and free peritoneal cells after wounding. A larger expression of alpha-smooth muscle actin was seen around the wound edges compared to unwounded tissue. Both alpha-smooth muscle actin and transforming growth factor-beta type II receptor were expressed during Days 0, 3, 5, 7, and 10. The expression of alpha-smooth muscle actin on Day 5 was > 100 times higher than on Day 0. Transforming growth factor-beta 1 was expressed in both membranes and free peritoneal cells of unoperated control animals but down-regulated after wounding, a finding that has not been reported previously. It reappeared on Days 7 and 10 in free peritoneal cells but not in perforated membranes. The enhanced expression of alpha-smooth muscle actin and down-regulation of transforming growth factor-beta 1 expression after wounding appears to be important phenomena in tissue contraction and repair.

Adenovector-mediated gene transfer of active transforming growth factor-beta1 induces prolonged severe fibrosis in rat lung

Transforming growth factor (TGF)-beta1 has been implicated in the pathogenesis of fibrosis based upon its matrix-inducing effects on stromal cells in vitro, and studies demonstrating increased expression of total TGF-beta1 in fibrotic tissues from a variety of organs. The precise role in vivo of this cytokine in both its latent and active forms, however, remains unclear. Using replication-deficient adenovirus vectors to transfer the cDNA of porcine TGF-beta1 to rat lung, we have been able to study the effect of TGF-beta1 protein in the respiratory tract directly. We have demonstrated that transient overexpression of active, but not latent, TGF-beta1 resulted in prolonged and severe interstitial and pleural fibrosis characterized by extensive deposition of the extracellular matrix (ECM) proteins collagen, fibronectin, and elastin, and by emergence of cells with the myofibroblast phenotype. These results illustrate the role of TGF-beta1 and the importance of its activation in the pulmonary fibrotic process, and suggest that targeting active TGF-beta1 and steps involved in TGF-beta1 activation are likely to be valuable antifibrogenic therapeutic strategies. This new and versatile model of pulmonary fibrosis can be used to study such therapies.

Cell types of secondary cataract: an immunohistochemical analysis with antibodies to cytoskeletal elements and macrophages

BACKGROUND

The study was carried out to identify cell types of secondary cataract after extracapsular cataract extraction and implantation of an intraocular lens.

METHODS

Twenty-five formalin-fixed, paraffin-embedded pseudophakic human eyes with secondary cataract, obtained at autopsy, were studied and compared to a specimen from an anterior subcapsular cataract with a panel of six monoclonal antibodies (MAbs, to vimentin, cytokeratin (CK) 8 and 18, desmin, alpha-smooth muscle actin, and the CD68 epitope of macrophages by the avidin-biotinylated peroxidase complex (ABC) method.

RESULTS

MAb Vim 3B4 to vimentin immunolabeled spindle-shaped cells in 16 of 17 central plaques of secondary cataract as well as cells in all 16 Soemmering's ring cataracts. Spindle-shaped cells reacted with MAb CAM 5.2 to CK 8 in 13 of 18 eyes, but only one specimen was labeled with MAb CY-90 to CK 18. No immunoreaction was seen with MAb D33 to desmin, whereas MAb 1A4 to alpha-smooth muscle actin immunolabeled spindle-shaped cells in 15 of 18 plaques of secondary cataract. Macrophages were seen with MAb PG-M1 in 13 of 19 secondary cataracts. In the anterior subcapsular cataract, spindle-shaped cells under a wrinkled but otherwise intact capsule reacted with MAb Vim 3B4 to vimentin, MAb CAM 5.2 to CK 8, and MAb 1A4 to alpha-smooth muscle actin.

CONCLUSION

Spindle-shaped cells in secondary and anterior subcapsular cataracts react with antibodies to vimentin, CK 8 and alpha-smooth muscle actin, suggesting them to be metaplastic epithelial cells that derive from the lens epithelium. alpha-Smooth muscle actin persists in them at least 10 years postoperatively, but CK 8 starts to disappear after 3 years. Macrophages are one possible modulator of this transdifferentiation.

Myofibroblast accumulation induced by transforming growth factor-beta is involved in the pathogenesis of nasal polyps

Myofibroblasts that express alpha-smooth muscle actin (alpha-SMA) are detected in many chronic inflammatory diseases. Transforming growth factor-beta (TGF-beta) is a potent inducer of myofibroblast accumulation in tissues. In this study, scattered myofibroblasts and TGF-beta were quantified and localized in nasal polyps (NPs) and normal nasal mucosa (NM). NPs were sampled in 16 patients during ethmoidectomy and NM was obtained from 10 control subjects during rhinoplasty. alpha-SMA and TGF-beta were detected using immunohistochemistry and the numbers of labeled cells were quantified (alpha-SMA and TGF-beta indices) and compared between NPs and NM. In eight NPs, in which the pedicle was preserved, alpha-SMA and TGF-beta were evaluated and compared in the pedicle, central, and tip areas. Finally, TGF-beta expression was compared between low (zone 1), moderate (zone 2), and high (zone 3) zones of alpha-SMA positivity. alpha-SMA and TGF-beta indices were significantly higher in NPs than in NM. In the eight selected NPs, alpha-SMA-positive cells were significantly more abundant in the pedicle than in the central and tip areas, whereas TGF-beta-positive cells were significantly more numerous in the pedicle than in the tip area. The number of TGF-beta-positive cells was significantly higher in zone 3 than in zone 1 of alpha-SMA positivity. Myofibroblasts, which are abundant in NPs but rare in NM, could be involved in the growth of NPs by inducing extracellular matrix accumulation. The local development of myofibroblasts in NPs could be controlled by TGF-beta, locally produced by inflammatory cells.

Myofibroblast persistence in fetal sheep wounds is associated with scar formation

The scarless repair capabilities of the fetus are influenced by the size of the wound and the gestational age of the fetus. Whereas small wounds heal scarlessly, large wounds in the same fetus heal with scar. Myofibroblasts are specialized fibroblasts that express alpha-smooth muscle actin (alpha-SMA), a contractile cytoskeletal protein. The authors hypothesized that small fetal wounds that heal scarlessly will have a relative absence of myofibroblasts, whereas large wounds that heal with scar will have abundant myofibroblasts. In this study, an incisional wound and four punch biopsy wounds of 2, 4, 6, and 10 mm diameter were placed on the backs of 60- to 90-day-gestation fetal sheep (term, 145 days). Fourteen days after wounding, the healed fetal wounds were harvested, the repair morphology was determined (scarless, transitional repair, or scar), and the expression of alpha-SMA was analyzed by immunohistochemistry. In the second part of this study the authors analyzed the temporal expression of alpha-SMA in fetal wounds at 1, 2, 3, and 7 days after wounding in 70-day-gestation fetal sheep. In the 14-day wounds, the authors found that alpha-SMA was not expressed in any incisional or 2-mm wound that healed scarlessly, but it was expressed in all wounds that healed with scar. Overall, alpha-SMA expression strongly correlated with increasing wound size (P < .005). Myofibroblasts were seen as early as 24 hours after wounding, and at 3 and 7 days all wounds showed strong expression of alpha-SMA. These results demonstrate that although myofibroblasts are induced early in fetal wound repair, by 14 days there is a notable lack of myofibroblasts in wounds that heal scarlessly and an abundance of myofibroblasts in those wounds that scar. By determining the factors that regulate the disappearance of the myofibroblast in scarless fetal wounds, the authors hope to gain new insights into the mechanisms of scarless fetal repair.

Expression of smooth muscle alpha-actin in mesenchymal cells during formation of avian endocardial cushion tissue: a role for transforming growth factor beta3

During early cardiac morphogenesis, outflow tract (OT) and atrio-ventricular (AV) endothelial cells differentiate into mesenchymal cells, which have characteristics of smooth muscle-like myofibroblasts, and which form endocardial cushion tissue, the primordia of valves, and septa in the adult heart. During this embryonic event, transforming growth factor beta3 (TGF beta3) is an essential element in the progression of endothelial-transformation into mesenchyme. TGF beta(s) are known to be a potent inducer for mesodermal differentiation and a promoter for differentiation of endothelial cells into smooth muscle-like cells. Using a monoclonal antibody against smooth muscle-specific alpha-actin (SMA), we examined the immunohistochemical staining of this form of actin in avian endocardial cushion tissue formation. To determine whether TGF beta3 initiates the expression of SMA, the pre-migratory AV endothelial monolayer was cultured with or without chicken recombinant TGF beta3 and the expression of SMA was examined immunochemically. Migrating mesenchymal cells expressed SMA beneath the cell surface membrane. These cells showed a reduction of endothelial specific marker antigen, QH1. Stationary endothelial cells did not express SMA. The deposition of SMA in the mesenchymal tissue persisted until the end of the fetal period. Pre-migratory endothelial cells cultured in complete medium (CM199) that contained TGF beta3 expressed SMA, whereas cells cultured in CM199 alone did not. At the onset of the endothelial-mesenchymal transformation, migrating mesenchymal cells express SMA and the expression of this form of actin is upregulated by TGF beta3. The induction of the expression of SMA by TGF beta3 is one of the initial events in the cytoskeletal reorganization in endothelial cells which separate from one another during the initial phenotypic change associated with the endothelial-mesenchymal transformation.

High lung inflation increases mRNA levels of ECM components and growth factors in lung parenchyma

Remodeling of pulmonary capillaries occurs after chronic increases in capillary pressure (e.g., mitral stenosis). Also, remodeling of pulmonary arteries begins within 4 h of increased wall stress and is endothelium dependent. We have previously shown that high lung inflation increases wall stress in pulmonary capillaries. This study was designed to determine whether high lung inflation induces remodeling of the extracellular matrix (ECM) in lung parenchyma. Open-chest rabbits were ventilated for 4 h with 9-cmH2O positive end-expiratory pressure (PEEP) on one lung and 1-cmH2O PEEP on the other (High-PEEP group), or with 2-cmH2O PEEP on both lungs (Low-PEEP group). An additional untreated control group was also included. We found increased levels of mRNA in both lungs of High-PEEP rabbits (compared with both the Low-PEEP and untreated groups) for alpha1(III) and alpha2(IV) procollagen, fibronectin, basic fibroblast growth factor, and transforming growth factor-beta1. In contrast, alpha2(I) procollagen and vascular endothelial growth factor mRNA levels were not changed. We conclude that high lung inflation for 4 h increases mRNA levels of ECM components and growth factors in lung parenchyma.

Transforming growth factor beta 1 and interleukin 4 induced alpha smooth muscle actin expression and myofibroblast-like differentiation in human synovial fibroblasts in vitro: modulation by basic fibroblast growth factor

OBJECTIVE

To discover if alpha smooth muscle actin expression and myofibroblastic differentiation are induced in synovial fibroblasts by cytokines found in the inflamed RA joint.

METHODS

Immunofluorescent microscopy and western blotting were used to examine different cultures of human synovial fibroblasts for expression of alpha actin in the presence of the cytokines transforming growth factor beta (TGF beta 1), interleukin 1 alpha (IL1 alpha), IL4, IL6, tumour necrosis factor alpha (TNF alpha), and basic fibroblast growth factor (FGF).

RESULTS

A small but significant population of cells (14.4 +/- 12.9%) expressed alpha actin under standard culture conditions. Upon treatment with TGF beta 1 there was a pronounced increase in the number of cells expressing alpha actin (68.1 +/- 5.49%), accompanied by a change in morphology to a myofibroblast-like phenotype. Other cytokines found within the inflamed joint such as IL1, TNF alpha, IL6, and basic FGF failed to induce alpha actin expression. However, IL4, which is normally absent or only present at low concentrations in the RA joint had a similar effect to TGF beta 1. It was also found that basic FGF inhibited the induction of alpha actin expression by TGF beta 1 and IL4.

CONCLUSION

In the presence of TGF beta 1 or IL4, fibroblasts derived from synovial tissue or synovial fluid are induced to differentiate into myofibroblast-like cells containing the alpha smooth muscle form of actin. This differentiation is inhibited by basic FGF. It is suggested that the balance between these particular cytokines may be important in the modulation of fibroblast behaviour, which could have significant effects on joint repair mechanisms and the generation of fibrous tissue within the rheumatoid joint.

Remodeling of autologous saphenous vein grafts. The role of perivascular myofibroblasts

BACKGROUND

Aortocoronary saphenous vein grafts (SVGs) undergo structural changes that render them susceptible to atherosclerosis. Accordingly, the origin of neointimal hyperplasia-was examined in porcine arterialized SVGs to determine the mechanism of vein graft remodeling.

METHODS AND RESULTS

At 2 to 4 days after surgery, the percentage of cells lacking differentiation markers characteristic for smooth muscle (SM) cells (ie, alpha-SM actin, desmin, and SM myosin) increased within the media of SVGs interposed in the carotid arteries (P < .001). At 7 to 14 days, these cells acquired a differentiated phenotype (ie, alpha-SM-actin positive/ variable desmin/SM-myosin negative) and accumulated in the neointima. At 3 months, the neointima was positive for alpha-SM actin but mostly negative for desmin, which contrasted with medial SMCs that were invariably positive for alpha-SM actin, desmin, and SM myosin. To determine the role of nonmuscle cells in the above process, perivascular wound fibroblasts were selectively labeled and found to translocate through the media of newly placed SVGs, contributing to neointimal formation. These migrating cells differentiated to myofibroblasts exhibiting sustained alpha-SM-actin expression. The intima of human SVGs, retrieved during repeat aortocoronary bypass surgery, exhibited the profile of cytoskeletal proteins that resembled myofibroblasts seen in porcine SVGs.

CONCLUSIONS

Perivascular fibroblasts may infiltrate injured media of arterialized SVGs, differentiate to myofibroblasts (acquiring alpha-SM actin), and contribute to vein graft remodeling. The similarities between porcine and human SVGs regarding the repertoire of cytoskeletal proteins suggest the involvement of myofibroblasts in graft remodeling in the clinical setting.

General principles of wound healing

Wound healing is a complex process involving different biologic and immunologic systems. Despite improvements in diagnostics and therapy, wound failures remain a clinical problem. The approach to a nonhealed wound is an interdisciplinary challenge that should not be underestimated. Better understanding of the complex wound-healing cascade helps our approach to wound healing and its possible failure. Manipulations of the involved immunologic features offer future therapeutic strategies.

Myofibroblasts and arteriolar sclerosis in human diabetic nephropathy

We examined the biopsy specimens of 62 patients with diabetic nephropathy to establish whether the myofibroblast (MF) has a role in progressive interstitial fibrosis and to ascertain whether a relationship existed between MF activity and severity of arteriolosclerosis. MF were identified by morphology and alpha smooth muscle actin (alpha SMA) immunostaining. Analysis of vascular injury was performed by counting the number of interstitial arterioles after staining endothelial cells with von Willebrand factor (VWF) antibody. Arteriosclerosis was quantified by using a computer-aided image analyzer to measure the arteriolar wall surface and total arteriolar surface area, and the ratio of wall to total surface area was expressed as the index of arteriosclerosis (IA). Fractional area of interstitium (IFA), alpha SMA, and collagen III (Coll III) were quantitated by point counting. Results were related to structural and functional parameters using rank correlation coefficients. There was a strong correlation between IFA and Coll III staining (r = 0.83; P < 0.001). The alpha SMA staining correlated with IFA (r = 0.56; P < 0.001) and Coll III (r = 0.47; P < 0.001), and there were significant correlations between alpha SMA and total urinary protein (r = 0.47; P < 0.001), renal function (plasma creatinine) at time of biopsy (r = 0.51; P < 0.001), and the percent change in plasma creatinine after 4 years (delta Cr) (r = 0.37; P = 0.01). The IA correlated significantly with Coll III (r = 0.29; P = 0.02), glomerular filtration rate (GFR) (r = 0.39; P = 0.008), and creatinine (r = 0.33; P = 0.01), but no correlation was observed between alpha SMA and IA (r = 0.16; P = 0.23) or IA and delta Cr (r = -0.04; P = 0.6). Strong correlations could be shown between arteriolar density, IFA (r = 0.75; P < 0.001), alpha SMA (r = -0.36; P = 0.034), and Coll III (r = -0.66; P < 0.0001). The MF appears to have a significant role in the progression of diabetic nephropathy. Ischemia secondary to arteriosclerosis may contribute to interstitial fibrosis through fibroblast modulation into MF.

Induction of smooth muscle cell phenotype in cultured human prostatic stromal cells

Stromal cells are key regulators of growth and differentiation in the adult human prostate. Alterations in the stroma are believed to initiate the development of benign prostatic hyperplasia, and stromal-epithelial interactions may have a role in malignant progression. The prostatic stroma is composed of two major cell types, smooth muscle cells and fibroblasts. Cell cultures from the prostatic stroma have been established by several investigators, but the phenotype of these cells has not been extensively characterized and it is not clear whether they are fibroblastic or smooth muscle-like. In this study, the response of stromal cells cultured from normal prostatic tissues to transforming growth factor-beta (TGF beta) was investigated. We confirmed a previous report that TGF beta inhibited the growth of prostatic stromal cells in serum-containing medium, and showed that inhibition also occurred in serum-free medium. Growth inhibition by TGF beta was irreversible after 24 to 72 h of exposure. In the absence of TGF beta, cells were fibroblastic and expressed vimentin and fibronectin but little alpha-smooth muscle actin. After 3 days of exposure to 1 ng/ml of TGF beta, the majority of cells expressed alpha-smooth muscle actin and desmin, as demonstrated by immunocytochemistry and immunoblot analysis. This effect was specific and alpha-smooth muscle actin was not induced by two other growth-inhibitory factors, retinoic acid or 1,25-dihydroxyvitamin D3. These results suggest that TGF beta is an important regulator of growth and differentiation of prostatic stromal cells and that a smooth muscle cell phenotype is promoted in the presence of TGF beta.

A transforming growth factor beta (TGFbeta) control element drives TGFbeta-induced stimulation of smooth muscle alpha-actin gene expression in concert with two CArG elements

The goal of the present study was to determine the molecular mechanism whereby transforming growth factor beta (TGFbeta) increases smooth muscle (SM) alpha-actin expression. Confluent, growth-arrested rat aortic smooth muscle cells (SMC) were transiently transfected with various SM alpha-actin promoter/chloramphenicol acetyltransferase deletion mutants and stimulated with TGFbeta (2.5 ng/ml). Results demonstrated that the first 125 base pairs of the SM alpha-actin promoter were sufficient to confer TGFbeta responsiveness. Three cis elements were shown to be required for TGFbeta inducibility: two highly conserved CArG boxes, designated A (-62) and B (-112) and a novel TGFbeta control element (TCE) (-42). Mutation of any one of these elements completely abolished TGFbeta-induced reporter activity. Results of electrophoretic mobility shift assays demonstrated that nuclear extracts from TGFbeta-treated SMC enhanced binding activity of serum response factor to the CArG elements and binding of an as yet unidentified factor to the TCE. Northern analysis showed that TGFbeta also stimulated transcription of two other SM (SM myosin heavy chain) differentiation marker genes, SM myosin heavy chain and h1 calponin, whose promoters also contained a TCE-like element. In summary, we identified a TGFbeta response element in the SM alpha-actin promoter that may contribute to coordinate regulation of expression of multiple cell-type specific proteins during SMC differentiation.

Wound healing--aiming for perfect skin regeneration

The healing of an adult skin wound is a complex process requiring the collaborative efforts of many different tissues and cell lineages. The behavior of each of the contributing cell types during the phases of proliferation, migration, matrix synthesis, and contraction, as well as the growth factor and matrix signals present at a wound site, are now roughly understood. Details of how these signals control wound cell activities are beginning to emerge, and studies of healing in embryos have begun to show how the normal adult repair process might be readjusted to make it less like patching up and more like regeneration.

Fetal and postnatal sera differentially modulate human dermal fibroblast phenotypic and functional features in vitro

Fetal wounds heal without scar formation, fibrosis, or contracture. Compared with adult wounds, they are characterized by major differences in the extracellular matrix and the absence of myofibroblastic cells. The reasons for these differences are not well known and determination of factors affecting the absence of scarring in the fetus may lead to strategies for controlling adult pathological scarring. In the present study, we have assessed the effects of serum on the behavior of normal human dermal fibroblasts. Using an in vitro approach, we investigated the effects of fetal and adult serum on cell properties such as growth rate, collagen synthesis, gelatinase activities, and differentiation to myofibroblasts using biochemical, morphological, and ultrastructural parameters. We studied the induction of alpha-smooth muscle (alpha-SM) actin in fibroblasts, and its correlation with increased collagen gel contraction by the cells. Our results showed that, compared with FBS (fetal bovine serum), postnatal calf serum (PCS) decreased mitogenic activity and collagenase synthesis but not collagen synthesis. Furthermore, cells cultured with PCS differentiated to myofibroblasts with an increase in cell diameter, number of stress fibers, alpha-SM actin expression, and collagen gel contraction. To characterize the molecules involved in this differentiation process, the amount of transforming growth factor beta (TGFbeta) in FBS and PCS was determined and the effect of neutralizing anti-TGFbeta antibody was evaluated. It was determined that FBS contained more TGFbeta than PCS, but that essentially all the TGFbeta was latent in both sera. However, results obtained with anti-TGFbeta antibody show that active TGFbeta is present when human dermal fibroblasts are cultured with medium containing PCS. These results suggest that, in the presence of PCS but not FBS, the cells either produce active TGFbeta or an enzyme that is able to activate latent serum TGFbeta. Alternatively, sera may contain two different forms of latent TGFbeta, the PCS form being activated by the dermal fibroblast cells. A similar mechanism may be involved, at least in part, in skin wound healing and may underlie the appearance of myofibroblasts in postnatal wounds.

Ageing and wounds. Part 1: Foetal and postnatal healing

The first in a two-part series of reviews outlines the physiology of wound healing in the normal adult and discusses how it differs from that of the foetus.

Expression of nonmuscle myosin heavy chain-B isoform in the vessel wall of porcine coronary arteries after balloon angioplasty

Nonmuscle myosin heavy chain-B isoform (NMMHC-B) is expressed by proliferating vascular smooth muscle cells (SMCs), and its expression in primary lesions has been proposed to be predictive of restenosis after atherectomy. The present study was designed to study the time-course expression of NMMHC-B after angioplasty of porcine coronary arteries by in situ hybridization and immunohistochemistry. Domestic juvenile swine underwent percutaneous transluminal coronary angioplasty (PTCA) of the left anterior descending and circumflex coronary arteries with standard clinical angioplasty catheters. To identify proliferating cells, 5'-bromo-2'-deoxyuridine (BrdU) was administered and detected by immunohistochemistry on serial sections. Vessels were examined at 3, 7, and 14 days after balloon angioplasty, and uninjured coronary vessels were used as controls. Normal arteries showed hybridization to 35S-labeled NMMHC-B riboprobes localized mainly in the medial layer. NMMHC-B expression in the adventitia was markedly increased 3 days after balloon angioplasty. Seven and 14 days after injury, NMMHC-B mRNA-containing cells were localized in the adventitia and neointima at the arterial injury site. Cell proliferation, as indicated by BrdU staining, colocalized with NMMHC-B mRNA expression 3 and 7 days after angioplasty. These data indicate that cells proliferating in the adventitia and neointima express NMMHC-B; however, its expression is not limited to the proliferative state, since NMMHC-B mRNA was also found in quiescent SMCs of normal coronary arteries and in nonproliferating adventitial and neointimal cells 14 days after angioplasty.

Transforming growth factor-beta 1 modulates myofibroblastic phenotype of rat palatal fibroblasts in vitro

The effects of transforming growth factor-beta 1 (TGF-beta 1) on normal rat palatal fibroblasts in vitro were investigated in the present study in order to unravel the precise mechanisms by which the phenotypic modulation of fibroblasts occurs during the scar formation process. TGF-beta 1 dramatically changed the morphology of normal palatal fibroblasts from polygonal into an elongated shape, which was very similar to that of fibroblasts derived from experimental immature scar tissue in rat palatal mucosa. This morphological transition was concomitant with an increase in the expression of alpha-smooth muscle (alpha-SM) actin protein, a marker for myofibroblasts, when determined by immunocytochemistry. An immunoblot study also revealed that alpha-SM actin expression in palatal fibroblasts became evident after 24 h of TGF-beta 1 treatment and increased time-dependently up to 72 h. Northern blot analysis showed that TGF-beta 1 stimulated endogenous TGF-beta 1 mRNA expression in palatal fibroblasts within 24 h. Neither epidermal growth factor nor basic fibroblast growth factor had any effect on either alpha-SM actin expression or TGF-beta 1 mRNA expression. Pretreatment of palatal fibroblasts with TGF-beta 1 significantly increased the contractile capacity in a three-dimensional collagen gel culture, even when the culture medium was deprived of TGF-beta 1 for 72 h of the experimental period. Moreover, the contractility of scar fibroblasts, which highly expressed alpha-SM actin protein and TGF-beta 1 mRNA, was significantly lowered by a neutralizing antibody to TGF-beta 1. These data strongly suggest that TGF-beta 1 is a potential inducer of phenotypic expression of myofibroblasts in palatal fibroblasts and that auto-induction of TGF-beta 1 mRNA expression may play an important role in the scar formation process in palatal mucosa.