Myofibroblasts: molecular crossdressers

TWIST1 expression is associated with high-risk neuroblastoma and promotes primary and metastatic tumor growth

The embryonic transcription factors TWIST1/2 are frequently overexpressed in cancer, acting as multifunctional oncogenes. Here we investigate their role in neuroblastoma (NB), a heterogeneous childhood malignancy ranging from spontaneous regression to dismal outcomes despite multimodal therapy. We first reveal the association of TWIST1 expression with poor survival and metastasis in primary NB, while TWIST2 correlates with good prognosis. Secondly, suppression of TWIST1 by CRISPR/Cas9 results in a reduction of tumor growth and metastasis colonization in immunocompromised mice. Moreover, TWIST1 knockout tumors display a less aggressive cellular morphology and a reduced disruption of the extracellular matrix (ECM) reticulin network. Additionally, we identify a TWIST1-mediated transcriptional program associated with dismal outcome in NB and involved in the control of pathways mainly linked to the signaling, migration, adhesion, the organization of the ECM, and the tumor cells versus tumor stroma crosstalk. Taken together, our findings confirm TWIST1 as promising therapeutic target in NB.

Cilia, Centrosomes and Skeletal Muscle

Primary cilia are non-motile, cell cycle-associated organelles that can be found on most vertebrate cell types. Comprised of microtubule bundles organised into an axoneme and anchored by a mature centriole or basal body, primary cilia are dynamic signalling platforms that are intimately involved in cellular responses to their extracellular milieu. Defects in ciliogenesis or dysfunction in cilia signalling underlie a host of developmental disorders collectively referred to as ciliopathies, reinforcing important roles for cilia in human health. Whilst primary cilia have long been recognised to be present in striated muscle, their role in muscle is not well understood. However, recent studies indicate important contributions, particularly in skeletal muscle, that have to date remained underappreciated. Here, we explore recent revelations that the sensory and signalling functions of cilia on muscle progenitors regulate cell cycle progression, trigger differentiation and maintain a commitment to myogenesis. Cilia disassembly is initiated during myoblast fusion. However, the remnants of primary cilia persist in multi-nucleated myotubes, and we discuss their potential role in late-stage differentiation and myofiber formation. Reciprocal interactions between cilia and the extracellular matrix (ECM) microenvironment described for other tissues may also inform on parallel interactions in skeletal muscle. We also discuss emerging evidence that cilia on fibroblasts/fibro-adipogenic progenitors and myofibroblasts may influence cell fate in both a cell autonomous and non-autonomous manner with critical consequences for skeletal muscle ageing and repair in response to injury and disease. This review addresses the enigmatic but emerging role of primary cilia in satellite cells in myoblasts and myofibers during myogenesis, as well as the wider tissue microenvironment required for skeletal muscle formation and homeostasis.

Mechanical and Immunological Regulation in Wound Healing and Skin Reconstruction

In the past decade, a new frontier in scarless wound healing has arisen because of significant advances in the field of wound healing realised by incorporating emerging concepts from mechanobiology and immunology. The complete integumentary organ system (IOS) regeneration and scarless wound healing mechanism, which occurs in specific species, body sites and developmental stages, clearly shows that mechanical stress signals and immune responses play important roles in determining the wound healing mode. Advances in tissue engineering technology have led to the production of novel human skin equivalents and organoids that reproduce cell–cell interactions with tissue-scale tensional homeostasis, and enable us to evaluate skin tissue morphology, functionality, drug response and wound healing. This breakthrough in tissue engineering has the potential to accelerate the understanding of wound healing control mechanisms through complex mechanobiological and immunological interactions. In this review, we present an overview of recent studies of biomechanical and immunological wound healing and tissue remodelling mechanisms through comparisons of species- and developmental stage-dependent wound healing mechanisms. We also discuss the possibility of elucidating the control mechanism of wound healing involving mechanobiological and immunological interaction by using next-generation human skin equivalents.

Pulmonary persistence of graphene nanoplatelets may disturb physiological and immunological homeostasis

Accumulated evidence suggests that chronic pulmonary accumulation of harmful particles cause adverse pulmonary and systemic health effects. In our previous study, most of the graphene nanoplatelet (GNP) remained in the lung until 28 days after a single instillation. In this study, we sought to evaluate the local and systemic health effect after a long pulmonary persistence of GNP. As expected, GNP remained in the lung on day 90 after a single intratracheal instillation (1.25, 2.5 and 5 mg kg^-1 ). In the lung exposed at the highest dose, the total number of cells and the percentage of lymphocytes significantly increased in the BAL fluid with an increase in both the number of GNP-engulfed macrophages and the percentage of apoptotic cells. A Th1-shifted immune response, the elevated chemokine secretion and the enhanced expression of cytoskeletal-related genes were observed. Additionally, the expression of natriuretic-related genes was noteworthy altered in the lungs. Moreover, the number of white blood cells (WBC) and the percentage of macrophages and neutrophils clearly increased in the blood of mice exposed to a 5-mg kg^-1 dose, whereas total protein, BUN and potassium levels significantly decreased. In conclusion, we suggest that the long persistence of GNP in the lung may cause adverse health effects by disturbing immunological- and physiological-homeostasis of our body. Copyright © 2016 John Wiley & Sons, Ltd.

The myogenic electric organ of Sternopygus macrurus: a non-contractile tissue with a skeletal muscle transcriptome

In most electric fish species, the electric organ (EO) derives from striated muscle cells that suppress many muscle properties. In the gymnotiform Sternopygus macrurus, mature electrocytes, the current-producing cells of the EO, do not contain sarcomeres, yet they continue to make some cytoskeletal and sarcomeric proteins and the muscle transcription factors (MTFs) that induce their expression. In order to more comprehensively examine the transcriptional regulation of genes associated with the formation and maintenance of the contractile sarcomere complex, results from expression analysis using qRT-PCR were informed by deep RNA sequencing of transcriptomes and miRNA compositions of muscle and EO tissues from adult S. macrurus. Our data show that: (1) components associated with the homeostasis of the sarcomere and sarcomere-sarcolemma linkage were transcribed in EO at levels similar to those in muscle; (2) MTF families associated with activation of the skeletal muscle program were not differentially expressed between these tissues; and (3) a set of microRNAs that are implicated in regulation of the muscle phenotype are enriched in EO. These data support the development of a unique and highly specialized non-contractile electrogenic cell that emerges from a striated phenotype and further differentiates with little modification in its transcript composition. This comprehensive analysis of parallel mRNA and miRNA profiles is not only a foundation for functional studies aimed at identifying mechanisms underlying the transcription-independent myogenic program in S. macrurus EO, but also has important implications to many vertebrate cell types that independently activate or suppress specific features of the skeletal muscle program.

Fetal Rat Gubernaculum Mesenchymal Cells Adopt Myogenic and Myofibroblast-Like Phenotypes

PURPOSE

Gubernaculum-cremaster complex development is hormonally regulated and abnormal in a cryptorchid rat model. Using cell tracking techniques and imaging we studied myogenic phenotypes and fates in the fetal rat gubernaculum-cremaster complex.

MATERIALS AND METHODS

Embryonic day 17 gubernaculum-cremaster complexes were labeled with CellTracker™ or the DNA synthesis marker EdU (5-ethynyl-2'-deoxyuridine), or immobilized in Matrigel® and grown in culture. Embryonic day 17 to 21 gubernaculum-cremaster complex sections and cells were imaged using wide field and deconvolution immunofluorescence microscopy, and muscle and/or myofibroblast specific antibodies. Deconvolved image stacks were used to create a 3-dimensional model of embryonic day 21 gubernaculum-cremaster complex muscle.

RESULTS

PAX7 (paired box 7) positive and myogenin positive muscle precursors were visible in a desmin-rich myogenic zone between muscle layers that elongated and became thicker during development. Gubernaculum-cremaster complex inner mesenchymal cells expressed desmin and αSMA (α smooth muscle actin) at lower levels than in the myogenic zone. After pulse labeling with CellTracker or EdU mesenchymal cells became incorporated into differentiated muscle. Conversely, mesenchymal cells migrated beyond Matrigel immobilized gubernaculum-cremaster complexes, expressed PAX7 and fused to form striated myotubes. Mesenchymal gubernaculum-cremaster complex cell lines proliferated more than 40 passages and showed contractile behavior but did not form striated muscle. Our 3-dimensional gubernaculum-cremaster complex model had 2 orthogonal ventral layers and an arcing inner layer of muscle.

CONCLUSIONS

Our data suggest that mesenchymal cells in the peripheral myogenic zone of the fetal gubernaculum-cremaster complex contribute to formation of a distinctively patterned cremaster muscle. Nonmyogenic, desmin and αSMA positive gubernaculum-cremaster complex mesenchymal cells proliferate and have a myofibroblast-like phenotype in culture. Intrinsic mechanical properties of these divergent cell types may facilitate perinatal inversion of the gubernaculum-cremaster complex.

Idiopathic epiretinal membrane

BACKGROUND

Idiopathic epiretinal membrane (iERM) is a fibrocellular membrane that proliferates on the inner surface of the retina at the macular area. Membrane contraction is an important sight-threatening event and is due to fibrotic remodeling.

METHODS

Analysis of the current literature regarding the epidemiology, clinical features, and pathogenesis of iERM and fibrotic tissue contraction.

RESULTS

Epidemiologic studies report a relationship between iERM prevalence, increasing age, and posterior vitreous detachment. Clinically, iERM progresses through different stages characterized by an increased thickness and wrinkling of the membrane. Pathophysiologically, iERM formation is a fibrotic process in which myofibroblast formation and the deposition of newly formed collagens play key roles. Anomalous posterior vitreous detachment may be a key event initiating the formation of iERM. The age-related accumulation of advanced glycation end products may contribute to anomalous posterior vitreous detachment formation and may also influence the mechanical properties of the iERM.

CONCLUSION

Remodeling of the extracellular matrix at the vitreoretinal interface by aging and fibrotic changes, plays a significant role in the pathogenesis of iERM. A better understanding of molecular mechanisms underlying this process may eventually lead to the development of effective and nonsurgical approaches to treat and prevent vitreoretinal fibrotic diseases.

SMAD-independent down-regulation of caveolin-1 by TGF-β: effects on proliferation and survival of myofibroblasts

Transforming growth factor-β (TGF-β) mediates growth-inhibitory effects on most target cells via activation of the canonical SMAD signaling pathway. This growth-inhibitory activity may be coupled with cellular differentiation. Our studies demonstrate that TGF-β1 inhibits proliferation of primary, non-transformed human lung fibroblasts in association with the induction of myofibroblast differentiation. Differentiated myofibroblasts maintain the capacity to proliferate in response to exogenous mitogenic stimuli and are resistant to serum deprivation-induced apoptosis. These proliferative and anti-apoptotic properties of myofibroblasts are related, in part, to the down-regulation of caveolin-1 (Cav-1) by TGF-β1. Cav-1 down-regulation is mediated by early activation of p38 MAPK and does not require SMAD signaling. In contrast, myofibroblast differentiation is dependent on activation of the SMAD pathway, but not on p38 MAPK. Thus, combinatorial signaling by TGF-β1 of myofibroblast differentiation and down-regulation of Cav-1 by SMAD and p38 MAPK pathways, respectively, confer proliferative and apoptosis-resistant properties to myofibroblasts. Selective targeting of this SMAD-independent, p38-MAPK/Cav-1-dependent pathway is likely to be effective in the treatment of pathological conditions characterized by TGF-β signaling and myofibroblast activation.

Mechanisms of muscle gene regulation in the electric organ of Sternopygus macrurus

Animals perform a remarkable diversity of movements through the coordinated mechanical contraction of skeletal muscle. This capacity for a wide range of movements is due to the presence of muscle cells with a very plastic phenotype that display many different biochemical, physiological and morphological properties. What factors influence the maintenance and plasticity of differentiated muscle fibers is a fundamental question in muscle biology. We have exploited the remarkable potential of skeletal muscle cells of the gymnotiform electric fish Sternopygus macrurus to trans-differentiate into electrocytes, the non-contractile electrogenic cells of the electric organ (EO), to investigate the mechanisms that regulate the skeletal muscle phenotype. In S. macrurus, mature electrocytes possess a phenotype that is intermediate between muscle and non-muscle cells. How some genes coding for muscle-specific proteins are downregulated while others are maintained, and novel genes are upregulated, is an intriguing problem in the control of skeletal muscle and EO phenotype. To date, the intracellular and extracellular factors that generate and maintain distinct patterns of gene expression in muscle and EO have not been defined. Expression studies in S. macrurus have started to shed light on the role that transcriptional and post-transcriptional events play in regulating specific muscle protein systems and the muscle phenotype of the EO. In addition, these findings also represent an important step toward identifying mechanisms that affect the maintenance and plasticity of the muscle cell phenotype for the evolution of highly specialized non-contractile tissues.

Structural basis of multisite single-stranded DNA recognition and ACTA2 repression by purine-rich element binding protein B (Purβ)

A hallmark of dysfunctional fibroblast to myofibroblast differentiation associated with fibrotic disorders is persistent expression of ACTA2, the gene encoding the cyto-contractile protein smooth muscle α-actin. In this study, a PURB-specific gene knockdown approach was used in conjunction with biochemical analyses of protein subdomain structure and function to reveal the mechanism by which purine-rich element binding protein B (Purβ) restricts ACTA2 expression in mouse embryo fibroblasts (MEFs). Consistent with the hypothesized role of Purβ as a suppressor of myofibroblast differentiation, stable short hairpin RNA-mediated knockdown of Purβ in cultured MEFs promoted changes in cell morphology, actin isoform expression, and cell migration indicative of conversion to a myofibroblast-like phenotype. Promoter-reporter assays in transfected Purβ knockdown MEFs confirmed that these changes were attributable, in part, to derepression of ACTA2 transcription. To map the domains in Purβ responsible for ACTA2 repression, several recombinant truncation mutants were generated and analyzed based on hypothetical, computationally derived models of the tertiary and quaternary structure of Purβ. Discrete subdomains mediating sequence- and strand-specific cis-element binding, protein-protein interaction, and inhibition of a composite ACTA2 enhancer were identified using a combination of biochemical, biophysical, and cell-based assays. Our results indicate that the Purβ homodimer possesses three separate but unequal single-stranded DNA-binding modules formed by subdomain-specific inter- and intramolecular interactions. This structural arrangement suggests that the cooperative assembly of the dimeric Purβ repressor on the sense strand of the ACTA2 enhancer is dictated by the association of each subdomain with distinct purine-rich binding sites within the enhancer.

Targeting TGFβ signaling to inhibit fibroblast activation as a therapy for fibrosis and cancer: effect of halofuginone

The fibroblast to myofibroblast transition in wound healing, fibrosis and cancer has emerged as a viable target for pharmacological intervention. The myofibroblasts acquire specific characteristics because of differences in origin and localization, but also share common properties, such as TGFβ signaling. Halofuginone, an inhibitor of the Smad3 phosphorylation, downstream of the TGFβ signaling, inhibits the activation of fibroblasts and their ability to synthesize the extracellular matrix, regardless of their origin or location. Halofuginone prevented the new and stimulated resolution of pre-existing fibrosis of several organs and inhibited the development and progression of various tumors. Moreover, halofuginone synergizes with chemotherapy and reduces the need for high doses of toxic compounds without impairing the treatment efficacy. In fibrosis, where the myofibroblasts are the major participant, halofuginone can be used as a single therapy, whereas in cancer it should be considered in combination with other therapies that affect the tumor cells via different modalities.

Differences in transcriptional patterns of extracellular matrix, inflammatory, and myogenic regulatory genes in myofibroblasts, fibroblasts, and muscle precursor cells isolated from old male rat skeletal muscle using a novel cell isolation procedure

Aged skeletal muscle displays increased fibrosis and impaired regeneration. While it is not well characterized how skeletal muscle fibroblasts contribute to these phenomena, transforming growth factor-β1 (TGF-β1) and Delta/Notch signaling have been implicated to influence muscle regeneration. In this study, a unique combination of aging phenotypes is identified in differentiating fibroblasts (myofibroblasts), proliferating fibroblasts, and muscle precursor cells (MPCs) that characterize an impaired regenerative potential observed in aged skeletal muscle. Using a novel dual-isolation technique, that isolates fibroblasts and MPCs from the same rat skeletal muscle sample, and cell culture conditions of 5 % O(2) and 5 % CO(2), we report for the first time that myofibroblasts from 32-mo-old skeletal muscle, compared to 3-mo-old, display increased levels of mRNA for the essential extracellular matrix (ECM) genes, collagen 4α1 (83 % increase), collagen 4α2 (98 % increase), and laminin 2 (113 % increase), as well as increased levels of mRNA for the inflammatory markers, interleukin-6 (4.3-fold increase) and tumor necrosis factor α (3.2-fold increase), and TGF-β1 (84 % increase), whose protein controls proliferation and differentiation. Additionally, we demonstrate that proliferating fibroblasts from 32-mo-old skeletal muscle display increased levels of mRNA for the Notch ligand, Delta 1 (≥2.0-fold increase). Together, these findings suggest that increased expression of ECM and inflammatory genes in myofibroblasts from 32-mo-old skeletal muscle may contribute to the fibrogenic phenotype that impairs regeneration in aged skeletal muscle. Furthermore, we believe the novel dual-isolation technique developed here may be useful in studies that investigate communications among MPCs, fibroblasts, and myofibroblasts in skeletal muscle.

A novel single-chain-Fv antibody against connective tissue growth factor attenuates bleomycin-induced pulmonary fibrosis in mice

BACKGROUND AND OBJECTIVE

Connective tissue growth factor (CTGF) has been identified as playing critical roles in fibrosis and is a promising therapeutic target. In a previous study, we used a phage display library to develop a humanized single-chain variable fragment antibody (scFv) against CTGF. In the present study, the protective effect of anti-CTGF scFv against bleomycin (BL)-induced pulmonary fibrosis was investigated in mice.

METHODS

The expression of α-smooth muscle actin in human embryonic lung fibroblast (HELF) cells was analysed by western blotting. A mouse model of pulmonary fibrosis was established by tracheal injection of BL (5 mg/kg). Mice received anti-CTGF scFv (4 mg/kg, three times a week) by i.v. injection. The effects of anti-CTGF scFv were evaluated by leukocyte counts in BAL fluid, hydroxyproline measurements in lung tissue and pathological examination.

RESULTS

α-Smooth muscle actin expression was decreased in HELF cells treated with anti-CTGF scFv. Anti-CTGF scFv significantly reduced the numbers of inflammatory leukocytes (total and differential count) in BAL fluid, as well as the hydroxyproline content of lung tissue. The severity of alveolitis and fibrosis in the mouse model was markedly attenuated by treatment with anti-CTGF scFv.

CONCLUSIONS

Anti-CTGF scFv may potentially be developed as a useful inhibitor of pulmonary fibrosis.

Reversible differentiation of myofibroblasts by MyoD

Myofibroblasts participate in tissue repair processes in diverse mammalian organ systems. The deactivation of myofibroblasts is critical for termination of the reparative response and restoration of tissue structure and function. The current paradigm on normal tissue repair is the apoptotic clearance of terminally differentiated myofibroblasts; while, the accumulation of activated myofibroblasts is associated with progressive human fibrotic disorders. The capacity of myofibroblasts to undergo de-differentiation as a potential mechanism for myofibroblast deactivation has not been examined. In this report, we have uncovered a role for MyoD in the induction of myofibroblast differentiation by transforming growth factor-β1 (TGF-β1). Myofibroblasts demonstrate the capacity for de-differentiation and proliferation by modulation of endogenous levels of MyoD. We propose a model of reciprocal signaling between TGF-β1/ALK5/MyoD and mitogen(s)/ERK-MAPK/CDKs that regulate myofibroblast differentiation and de-differentiation, respectively. Our studies provide the first evidence for MyoD in controlling myofibroblast activation and deactivation. Restricted capacity for de-differentiation of myofibroblasts may underlie the progressive nature of recalcitrant human fibrotic disorders.

Fibrosis inhibition and muscle histopathology improvement in laminin-alpha2-deficient mice

In muscular dystrophies (MD) the loss of muscle and its ability to function are associated with fibrosis. We evaluated the efficacy of halofuginone in reducing fibrosis in the dy(2J)/dy(2J) mouse model of congenital MD. Mice were injected intraperitoneally with 5 microg of halofuginone 3 times a week for 5 or 15 weeks, starting at the age of 3 weeks. Halofuginone caused a reduction in collagen synthesis in hindlimb muscles. This was associated with reductions in the degenerated area, in cell proliferation, in the number of myofibers with central nuclei, with increased myofiber diameter, and with enhanced motor coordination and balance. Halofuginone caused a reduction in infiltrating fibroblasts that were located close to centrally nucleated myofibers. Our results suggest that halofuginone reduced the deleterious effects of fibrosis, thus improving muscle integrity. Halofuginone meets the criteria for a novel antifibrotic therapy for MD patients.

Noggin producing, MyoD-positive cells are crucial for eye development

A subpopulation of cells expresses MyoD mRNA and the cell surface G8 antigen in the epiblast prior to the onset of gastrulation. When an antibody to the G8 antigen was applied to the epiblast, labeled cells were later found in the ocular primordia and muscle and non-muscle forming tissues of the eyes. In the lens, retina and periocular mesenchyme, G8-positive cells synthesized MyoD mRNA and the bone morphogenetic protein inhibitor Noggin. MyoD expressing cells were ablated in the epiblast by labeling them with the G8 MAb and lysing them with complement. Their ablation in the epiblast resulted in eye defects, including anopthalmia, micropthalmia, altered pigmentation and malformations of the lens and/or retina. The right eye was more severely affected than the left eye. The asymmetry of the eye defects in ablated embryos correlated with differences in the number of residual Noggin producing, MyoD-positive cells in ocular tissues. Exogenously supplied Noggin compensated for the ablated epiblast cells. This study demonstrates that MyoD expressing cells serve as a Noggin delivery system to regulate the morphogenesis of the lens and optic cup.

Transcriptional regulation of hepatic stellate cells

Hepatic stellate cell (HSC) activation is a process of cellular transdifferentiation in which, upon liver injury, the quiescent vitamin A storing perisinusoidal HSC is converted into a wound-healing myofibroblast and acquires potent pro-inflammatory and pro-fibrogenic activities. This remarkable phenotypic transformation is underpinned by changes in the expression of a vast number of genes. In this review we survey current knowledge of the transcription factors that either control HSC activation or which regulate specific fibrogenic functions of the activated HSC such as collagen expression, proliferation and resistance to apoptosis.

Myofibroblasts in pulmonary and brain metastases of alveolar soft-part sarcoma: a novel target for treatment?

Alveolar soft-part sarcoma (ASPS) is a rare neoplasm with chromosomal translocation that results in ASPL-TFE3 fusion. It is a slow-growing lesion associated with a high incidence of pulmonary and brain metastases indicating poor survival. We demonstrated that the ASPS metastases include also stromal myofibroblasts. These cells proliferate, express smooth-muscle genes, and synthesize extracellular matrix proteins, all of which are characteristics of activated myofibroblasts. The tumor cells also exhibited stromal components such as transforming growth factor beta (TGFbeta)-dependent, hypoxia-regulated cytoglobin (stellate cell activation association protein, cytg/STAP) and prolyl 4-hydroxylase, a collagen cross-linking enzyme. The pulmonary ASPS myofibroblasts synthesize serum response factor (SRF), a repressor of Smad3-mediated TGFbeta signaling essential for myofibroblast differentiation and Smad3. The phosphorylated active Smad3 was found mostly in the tumor cells. The brain tumor cells express cytg/STAP, but in contrast to the lung metastases, they also express SRF, Smad3, and phospho-Smad3. Halofuginone, an inhibitor of myofibroblasts' activation and Smad3 phosphorylation, inhibited tumor development in xenografts derived from renal carcinoma cells harboring a reciprocal ASPL-TFE3 fusion transcript. This inhibition was associated with the inhibition of TGFbeta/SRF signaling, with the inhibition of myofibroblasts' activation, and with the complete loss in TFE3 synthesis by the tumor cells. These results suggest that the myofibroblasts may serve as a novel target for treatment of ASPS metastases.

AMP-activated protein kinase inhibits transforming growth factor-beta-induced Smad3-dependent transcription and myofibroblast transdifferentiation

In wound healing, myofibroblast transdifferentiation (MFT) is a metaplastic change in phenotype producing profibrotic effector cells that secrete and remodel the extracellular matrix. Unlike pathways that induce MFT, the molecular mechanisms that negatively regulate MFT are poorly understood. Here, we report that AMP-activated protein kinase (AMPK) blocks MFT in response to transforming growth factor-beta (TGFbeta). Pharmacological activation of AMPK inhibited TGFbeta-induced secretion of extracellular matrix proteins collagen types I and IV and fibronectin. AMPK activation also prevented induction of the myofibroblast phenotype markers alpha-smooth muscle actin and the ED-A fibronectin splice variant. AMPK activators did not prevent MFT in cells transduced with an adenovirus expressing dominant negative, kinase-dead AMPKalpha2. Moreover, AMPK activators did not inhibit MFT induction in AMPK(alpha1,2)(-/-) fibroblasts, demonstrating a requirement for AMPK(alpha) expression. Adenoviral transduction of constitutively active AMPK(alpha2) was sufficient to prevent TGFbeta-induced collagen I, alpha-smooth muscle actin, and ED-A fibronectin. AMPK did not reduce TGFbeta-stimulated Smad3 COOH-terminal phosphorylation and nuclear translocation, which are necessary for MFT. However, AMPK activation inhibited TGFbeta-induced transcription driven by Smad3-binding cis-elements. Consistent with a role for AMPK in transcriptional regulation, nuclear translocation of AMPKalpha2 correlated with the appearance of active AMPKalpha in the nucleus. Collectively, these results demonstrate that AMPK inhibits TGFbeta-induced transcription downstream of Smad3 COOH-terminal phosphorylation and nuclear translocation. Furthermore, activation of AMPK is sufficient to negatively regulate MFT in vitro.

Myogenic reprogramming of retina-derived cells following their spontaneous fusion with myotubes

Satellite cells are recognized as the main source for myoblasts in postnatal muscle. The possible participation of other cell types in myofiber maintenance remains a subject of debate. Here, we investigated the potential of vascular preparations from mouse retina to undergo myogenesis when cultured alone or with differentiated primary myogenic cultures. The choice of retina, an organ richly supplied with capillary network and anatomically separated from skeletal muscles, ensures that the vasculature preparation is devoid of satellite cells. We demonstrate that retina-derived cells spontaneously fuse with preexisting myotubes and contribute additional myonuclei, some of which initiate expression of muscle-specific genes after fusion. Myogenic differentiation of retinal cells prior to their fusion with preexisting myotubes was not detected. Although originating from vasculature preparations, nuclei undergoing myogenic reprogramming were contributed by cells that were neither endothelial nor blood borne. Our results suggest smooth muscle/pericytes as the possible source, and that myogenic reprogramming depends on the muscle specific transcription factor MyoD. Our studies provide insights into a novel avenue for myofiber maintenance, relying on nuclei of non-myogenic origin that undergo fusion and subsequent myogenic conversion within host myofibers. This process may support ongoing myofiber maintenance throughout life.

A role for TGF-beta1-induced cellular responses during wound healing of the non-scarring early human fetus?

Early human fetuses regenerate cutaneous wounds perfectly without scarring. However, transforming growth factor-beta1 (TGF-beta1), the cytokine linked with scarring in mature tissue, is also present during fetal wound repair, albeit transiently. We present a comparison of response to TGF-beta1 by fibroblasts derived from early human fetal skin (non-scarring) and their mature (scarring) postnatal counterparts, which revealed that although fetal fibroblasts do indeed differentiate into myofibroblasts, this response is altogether more rapid and short-lived. Fetal fibroblasts also failed to exhibit the TGF-beta1-induced increase in collagen (mRNA and protein) demonstrated by their postnatal counterparts. Fetal cells exhibited a comparatively short-lived or rapid phosphorylation of several components of the TGF-beta1 signaling pathways: Smad2/3 and c-Jun N-terminal kinase. Unlike quiescent postnatal fibroblasts, quiescent fetal fibroblasts also phosphorylated extracellular signal-regulated kinases in response to TGF-beta1. These altered responses to TGF-beta1 may well contribute to the transition between perfect regeneration and scar formation seen during development.

Structural components of the nonstriated contractile apparatuses in the Caenorhabditis elegans gonadal myoepithelial sheath and their essential roles for ovulation

Ovulation in the nematode Caenorhabditis elegans is regulated by complex signal transduction pathways and cell-cell interactions. Myoepithelial sheath cells of the proximal ovary are smooth muscle-like cells that provide contractile forces to push a mature oocyte into the spermatheca for fertilization. Although several genes that regulate sheath contraction have been characterized, basic components of the contractile apparatuses of the myoepithelial sheath have not been extensively studied. We identified major structural proteins of the contractile apparatuses of the myoepithelial sheath and characterized their nonstriated arrangement. Of interest, integrin and perlecan were found only at the dense bodies, whereas they localized to both dense bodies and M-lines in the striated body wall muscle. RNA interference of most of the myofibrillar components impaired ovulation in a soma-specific manner. Our results provide basic information that helps understanding the mechanism of sheath contraction during ovulation and establishing a new model to study morphogenesis of nonstriated muscle.

Microarray analysis of gene expression profile in the corpus cavernosum of hypercholesterolemic rats after chronic treatment with PDE5 inhibitor

Gene expression changes in the corpus cavernosum of hypercholesterolemic rats were not fully assessed, which were not previously known to be associated with hypercholesterolemia-related erectile dysfunction (ED). To provide molecular insight into pathophysiology of hypercholesterolemia-related ED and to investigate the effects of Udenafil, a phosphodiesterase type 5 (PDE5) inhibitor, on gene expression, we performed microarray gene expression analysis via gene discovery methods using GenoCheck platinum cDNA chip (Ansan, S. Korea). Sixteen male Sprague-Dawley rats were fed 2% cholesterol diet for 5 months. Half of them were orally treated with Udenafil (20 mg/kg/day) simultaneously. Eight age-matched rats fed normal diet were served as normal control. RNA was extracted from corpus cavernosum and microarray analysis was performed. Decreased erectile responses and hypercholesterolemia were observed in hypercholesterolemic control group. In microarray analysis, 122 candidate genes were noted to be altered based on the magnitude of expression changes, which includes 44 down-regulated and 78 up-regulated genes compared with the age-matched normal controls. These changes were, however, significantly attenuated by treatment with Udenafil. Out of the 78 up-regulated genes, 8 genes were significantly decreased by the chronic treatment with Udenafil. The altered genes were cytochrome oxidase biogenesis protein OXA1, skeletal muscle myosin heavy chain, lipophilin, fast skeletal muscle isoforms beta/alpha, myosin light chain 3, cytochrome c oxidase, adipocyte fatty acid binding protein and one EST gene. In contrast, among the 44 down-regulated genes, Kruppel-like factor 5 and cyclin D1 genes were increased after the Udenafil treatment. These results provide the molecular basis for understanding the pathogenesis of hypercholesterolemia-related ED and offer clues on determining the underlying action mechanism of a PDE5 inhibitor.

The skeletal muscle satellite cell: the stem cell that came in from the cold

The muscle satellite cell was first described and actually named on the basis of its anatomic location under the basement membrane surrounding each myofiber. For many years following its discovery, electron microscopy provided the only definitive method of identification. More recently, several molecular markers have been described that can be used to detect satellite cells, making them more accessible for study at the light microscope level. Satellite cells supply myonuclei to growing myofibers before becoming mitotically quiescent in muscle as it matures. They are then activated from this quiescent state to fulfill their roles in routine maintenance, hypertrophy, and repair of adult muscle. Because muscle is able to efficiently regenerate after repeated bouts of damage, systems must be in place to maintain a viable satellite cell pool, and it was proposed over 30 years ago that self-renewal was the primary mechanism. Self-renewal entails either a stochastic event or an asymmetrical cell division, where one daughter cell is committed to differentiation whereas the second continues to proliferate or becomes quiescent. This classic model of satellite cell self-renewal and the importance of satellite cells in muscle maintenance and repair have been challenged during the past few years as bone marrow-derived cells and various intramuscular populations were shown to be able to contribute myonuclei and occupy the satellite cell niche. This is a fast-moving and dynamic field, however, and in this review we discuss the evidence that we think puts this enigmatic cell firmly back at the center of adult myogenesis.

Cultured interstitial cells from human heart valves express both specific skeletal muscle and non-muscle markers

Cardiac valve interstitial cells are a phenotypically diverse and dynamic population, comprising myofibroblasts, fibroblasts and smooth muscle cells. To understand how these contribute to valve function and to optimize the choice of cells for seeding tissue-engineered valves, we are fingerprinting interstitial cells from all four human heart valves for useful phenotypic markers. We have begun by selecting markers indicated as of interest from previous work on myofibroblast-like cell lines. We show that interstitial cells express a variety of skeletal muscle contractile proteins and the skeletal muscle transcription factor myogenin, but not the related factors MyoD, myf-5 and MRF4, suggesting partial activation of the muscle programme in these cells. Expression of non-muscle isoforms of creatine kinase (CK-B) and AMP deaminase (AMPD2 and AMPD3) was found in contrast to muscle-restricted isoforms. Non-muscle isoforms of alpha- and beta-tropomyosins were detected specifically in contrast to skeletal muscle-specific isoforms. Several members of the Frizzled (FZD) family of Wnt receptors were also detected. In addition, intact cusps of all four valves from pig were capable of contacting to non-receptor and receptor-mediated stimulation in vitro. We conclude that interstitial cells from human heart valves express various sarcomeric proteins, and suggest that these cells have contractile potential due to a unique pattern of expression of both muscle-specific and non-muscle isoforms of metabolic and structural proteins. This may be under the control of myogenin, activated through specific Wnt/FZD signaling. Identifying such molecular markers could prove useful for engineering allogenic non-valve cell sources for seeding the synthetic valve.

Transforming growth factor-beta1 induces transdifferentiation of fibroblasts into myofibroblasts in hypoxic pulmonary vascular remodeling

The muscularization of non-muscular pulmonary arterioles is an important pathological feature of hypoxic pulmonary vascular remodeling. However, the origin of the cells involved in this process is still not well understood. The present study was undertaken to test the hypothesis that transforming growth factor-beta1 (TGF-beta1) can induce transdifferentiation of fibroblasts into myofibroblasts, which might play a key role in the muscularization of non-muscular pulmonary arterioles. It was found that mean pulmonary arterial pressure increased significantly after 7 d of hypoxia. Pulmonary artery remodeling index and right ventricular hypertrophy became evident after 14 d of hypoxia. The distribution of nonmuscular, partially muscular, and muscular vessels was significantly different after 7 d of hypoxia. Immunocytochemistry results demonstrated that the expression of a-smooth muscle actin was increased in intra-acinar pulmonary arteries with increasing hypoxic time. TGF-beta1 mRNA expression in pulmonary arterial walls was increased significantly after 14 d of hypoxia, but showed no obvious changes after 3 or 7 d of hypoxia. In pulmonary tunica adventitia and tunica media, TGF-beta1 protein staining was poorly positive in control rats, but was markedly enhanced after 3 d of hypoxia, reaching its peak after 7 d of hypoxia. The myofibroblast phenotype was confirmed by electron microscopy, which revealed microfilaments and a well-developed rough endoplasmic reticulum. Taken together, our results suggested that TGF-beta1 induces transdifferentiation of fibroblasts into myofibroblasts, which is important in hypoxic pulmonary vascular remodeling.

Crosslinked hyaluronan scaffolds as a biologically active carrier for valvular interstitial cells

Hyaluronic acid (HA), a major component of the cardiac jelly during heart morphogenesis, is a polysaccharide that upon modification can be photopolymerized into hydrogels. Previous work in our lab has found that photopolymerizable HA hydrogels are suitable scaffolds for the culture and proliferation of valvular interstitial cells (VICs), the most prevalent cell type in native heart valves. The physical properties of HA gels are easily modified through alteration in material crosslink density or by copolymerizing with other reactive macromolecules. Degradation products of HA gels and the starting macromers significantly increased VIC proliferation when added to cell cultures. With low molecular weight HA (<6700 Da) exhibiting greatest stimulation of VIC proliferation. Low molecular weight HA degradation products added to VIC cultures also resulted in a four-fold increase in total matrix production and a two-fold increase in elastin production over untreated controls. VIC internalization of HA, as shown by cellular uptake of fluorescently labeled HA, likely activates signaling cascades resulting in the biological responses seen here. Lastly, VICs encapsulated within HA hydrogels remained viable, and significant elastin production was observed after 6 weeks of culture. This work shows promise for the creation of a tissue-engineered heart valve utilizing the synergistic relationship between hyaluronic acid and VICs.

Designing scaffolds for valvular interstitial cells: cell adhesion and function on naturally derived materials

Valvular interstitial cells (VICs) possess many properties that make them attractive for use in the construction of a tissue-engineered valve; however, we have found that the surfaces to which VICs will adhere and spread are limited. For example, VICs adhere and spread on collagen and laminin-coated surfaces, but display altered morphology and do not proliferate. Interestingly, fibronectin (FN) was one adhesion protein that facilitated VIC adhesion and proliferation. Yet VICs did not spread on surfaces modified with RGD, a ubiquitous cell-adhesive peptide, nor with other FN-specific peptide sequences such as EILDV and PHSRN. Hyaluronic acid (HA) is a highly elastic polysaccharide that is involved in natural valve morphogenesis and possesses binding interactions with FN. Hyaluronic acid was modified to form photopolymerizable hydrogels, and VICs were found to spread and proliferate on HA-based gels, forming a confluent monolayer on the gels within 4 days. Modified HA retained its ability to specifically bind FN, allowing for the formation of gels containing both HA and FN. Valvular interstital cells cultured on HA surfaces displayed significantly increased production of extracellular matrix proteins, indicating that HA-based scaffolds may provide useful biological cues to stimulate heart valve tissue formation.

Tyrosine phosphorylation of the LDL receptor-related protein (LRP) and activation of the ERK pathway are required for connective tissue growth factor to potentiate myofibroblast differentiation

Renal myofibroblasts play a crucial role in the accumulation of excess extracellular matrix during renal fibrosis. Both transforming growth factor-beta1 (TGFbeta1) and connective tissue growth factor (CTGF) are important profibrotic growth factors, which interact in the pathogenesis of fibrosis. In this study, we demonstrate that CTGF alone has no influence on myofibroblast transformation and fibronectin secretion in kidney interstitial fibroblasts, whereas incubation of CTGF in combination with TGFbeta1 enhanced TGFbeta1 responses, including myofibroblast activation, de novo expression of alpha-SMA, and extracellular accumulation of fibronectin. CTGF induced tryrosine phosphorylation of the cytoplasmic domain of the low-density lipoprotein receptor-associated protein (LRP) in fibroblasts, and the LRP-antagonist, receptor-associated protein (RAP) inhibited CTGF-induced tryrosine phosphorylation of LRP. Inhibition of LRP signaling reduced CTGF-mediated synergistic induction of alpha-SMA protein. Furthermore, the potentiating action of CTGF was neither dependent on modulation of TGFbeta1-induced Smad2 phosphorylation and its association with Smad4, nor did it result from nuclear accumulation of activated Smad2. When TGFbeta1-pretreated fibroblasts were incubated with CTGF, activation of ERK1/2 MAPK signaling was observed. Inhibition of ERK activation by the MEK1 inhibitor PD98059 was associated with a reduction of CTGF-promoted alpha-SMA protein expression. Our in vitro studies provide evidence that CTGF potentiates TGFbeta1-mediated myofibroblast differentiation and activates differentiated myofibroblasts.

Valvular myofibroblast activation by transforming growth factor-beta: implications for pathological extracellular matrix remodeling in heart valve disease

The pathogenesis of cardiac valve disease correlates with the emergence of muscle-like fibroblasts (myofibroblasts). These cells display prominent stress fibers containing alpha-smooth muscle actin (alpha-SMA) and are believed to differentiate from valvular interstitial cells (VICs). However, the biological factors that initiate myofibroblast differentiation and activation in valves remain unidentified. We show that transforming growth factor-beta1 (TGF-beta1) mediates differentiation of VICs into active myofibroblasts in vitro in a dose-dependent manner, as determined by a significant increase in alpha-SMA and the dramatic augmentation of stress fiber formation and alignment. Additionally, TGF-beta1 and increased mechanical stress function synergistically to enhance contractility. In turn, contractile valve myofibroblasts exert tension on the extracellular matrix, resulting in a dramatic realignment of extracellular fibronectin fibrils. TGF-beta1 also inhibits valve myofibroblast proliferation without enhancing apoptosis. Our results are consistent with activation of a highly contractile myofibroblast phenotype by TGF-beta1 and are the first to connect valve myofibroblast contractility with pathological valve matrix remodeling. We suggest that the activation of contractile myofibroblasts by TGF-beta1 may be a significant first step in promoting alterations to the valve matrix architecture that are evident in valvular heart disease.

Mechanisms of pulmonary fibrosis

Tissue injury evokes highly conserved, tightly regulated inflammatory responses and less well-understood host repair responses. Both inflammation and repair involve the recruitment, activation, apoptosis, and eventual clearance of key effector cells. In this review, we propose the concept of pulmonary fibrosis as a dysregulated repair process that is perpetually "turned on" even though classical inflammatory pathways may be dampened or "switched off." Significant regional heterogeneity, with varied histopathological patterns of inflammation and fibrosis, has been observed in individual patients with idiopathic pulmonary fibrosis. We discuss environmental factors and host response factors, such as genetic susceptibility and age, that may influence these varied manifestations. Better understanding of the mechanisms of lung repair, which include alveolar reepithelialization, myofibroblast differentiation/activation, and apoptosis, should offer more effective therapeutic options for progressive pulmonary fibrosis.

Pathogenetic mechanisms in usual interstitial pneumonia/idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive, usually fatal, form of interstitial lung disease characterized by failure of alveolar re-epithelialization, persistence of fibroblasts/myofibroblasts, deposition of extracellular matrix, and distortion of lung architecture which ultimately results in respiratory failure. Clinical IPF is associated with a histopathological pattern of usual interstitial pneumonia (UIP) on surgical lung biopsy. Therapy for this disease with glucocorticoids and other immunomodulatory agents is largely ineffective and recent trials of newer anti-fibrotic agents have been disappointing. While the inciting event(s) leading to the initiation of scar formation in UIP remain unknown, recent advances in our understanding of the mechanisms underlying both normal and aberrant wound healing have shed some light on pathogenetic mechanisms that may play significant roles in this disease. Unlike other fibrotic diseases of the lung, such as those associated with collagen vascular disease, occupational exposure, or chemotherapeutic agents, UIP is not associated with a significant inflammatory response; rather, dysregulated epithelial-mesenchymal interactions predominate. Identification of pathways crucial to fibrogenesis might offer potentially novel therapeutic targets to slow or halt the progression of IPF. This review focuses on evolving concepts of cellular and molecular mechanisms in the pathogenesis of UIP/IPF.

Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF), also termed cryptogenic fibrosing alveolitis, is a clinicopathological syndrome characterised by cough, exertional dyspneoa, basilar crackles, a restrictive defect on pulmonary function tests, honeycombing on high-resolution, thin-section computed tomographic scans and the histological diagnosis of usual interstitial pneumonia on lung biopsy. The course is usually indolent but inexorable. Most patients die of progressive respiratory failure within 3-8 years of the onset of symptoms. Current therapies are of unproven benefit. Although the pathogenesis of IPF has not been elucidated, early concepts focused on lung injury leading to a cycle of chronic alveolar inflammation eventuating in fibrosis and destruction of the lung architecture. Anti-inflammatory therapies employing corticosteroids or immunosuppressive or cytotoxic agents have been disappointing. More recent hypotheses acknowledge that sequential alveolar epithelial cell injury is likely to be a key event in the pathogenesis of IPF, but the cardinal event is an aberrant host response to wound healing. In this context, abnormal epithelial-mesenchymal interactions, altered fibroblast phenotypes, exaggerated fibroblast proliferation, and excessive deposition of collagen and extracellular matrix are pivotal to the fibrotic process. Several clinical trials are currently underway or in the planning stages, and include drugs such as interferon-gamma 1b, pirfenidone, acetylcysteine, etanercept (a tumor necrosis factor-alpha antagonist), bosentan (an endothelin-1 receptor antagonist) and zileuton (a 5-lypoxygenase inhibitor). Future therapeutic strategies should be focused on alveolar epithelial cells aimed at enhancing re-epithelialisation and on fibroblastic/myofibroblastic foci, which play an essential role in the development of IPF. Stem cell progenitors of the alveolar epithelial cells and genetic and epigenetic therapies are attractive future approaches for this and other fibrotic lung disorders.

Expression of pericyte, mesangium and muscle markers in malignant rhabdoid tumor cell lines: differentiation-induction using 5-azacytidine

Malignant rhabdoid tumor (MRT) has been considered to have multiphenotypic diversity characteristics. Some MRTs exhibit a neural phenotype. However, it is still unclear whether MRT cells can display a skeletal muscle, smooth muscle or smooth muscle-like cell phenotype, like those of pericytes and mesangial cells. To determine if MRTs exhibit skeletal muscle cell or smooth muscle-like cell phenotypes, six MRT cell lines (TM87-16, STM91-01, TTC549, TTC642, YAM-RTK1 and TTC1240) were examined for markers of skeletal muscle (MyoD, myogenin, myf-5, myf-6, acetylcholine receptor-alpha, -beta and -gamma), smooth muscle (alpha-smooth muscle actin, SM-1 and SM22), and smooth muscle-like cells, such as pericytes (angiopoietin-1 and -2) and mesangial cells (megsin), using conventional RT-PCR, semi-quantitative PCR, western blotting and immunocytochemistry before and after differentiation-induction with 5-azacytidine. alpha-Smooth muscle actin and SM22 were detected in all six MRT cell lines, while MyoD and myf-5, crucial markers for skeletal myogenic determination, were not. The TM87-16 cell line expressed SM-1 and angiopoietin-1. TTC1240 also expressed angiopoietin-1. Interestingly, STM91-01 expressed megsin, a novel marker for mesangial cells, in addition to angiopoietin-1. Our results indicated that some MRTs exhibited smooth muscle and/or smooth muscle-like cell phenotypes and some renal MRTs might be of mesangial origin. Recently, smooth muscle and also smooth muscle-like cells have been considered to be of neuroectodermal origin. MRT can thus considered to belong to the category of primitive neuroectodermal tumors (PNETs) in the broad sense.

Skeletal myosin heavy chain function in cultured lung myofibroblasts

Myofibroblasts are unique contractile cells with both muscle and nonmuscle properties. Typically myofibroblasts are identified by the expression of alpha smooth muscle actin (ASMA); however some myofibroblasts also express sarcomeric proteins. In this study, we show that pulmonary myofibroblasts express three of the eight known sarcomeric myosin heavy chains (MyHCs) (IIa, IId, and embryonic) and that skeletal muscle myosin enzymatic activity is required for pulmonary myofibroblast contractility. Furthermore, inhibition of skeletal myosin activity and myofibroblast contraction results in a decrease in both ASMA and skeletal MyHC promoter activity and ASMA protein expression, suggesting a potential coupling of skeletal myosin activity and ASMA expression in myofibroblast differentiation. To understand the molecular mechanisms whereby skeletal muscle genes are regulated in myofibroblasts, we have found that members of the myogenic regulatory factor family of transcription factors and Ca(2+) - regulated pathways are involved in skeletal MyHC promoter activity. Interestingly, the regulation of skeletal myosin expression in myofibroblasts is distinct from that observed in muscle cells and suggests that cell context is important in its control.

Platelet-derived growth factor and its receptors are related to the progression of human muscular dystrophy: an immunohistochemical study

This study has examined the immunological localization of platelet-derived growth factor (PDGF)-A, PDGF-B, and PDGF receptor (PDGFR) alpha and beta to clarify their role in the progression of muscular dystrophy. Biopsied frozen muscles from patients with Duchenne muscular dystrophy (DMD), Becker muscular dystrophy (BMD), and congenital muscular dystrophy (CMD) were analysed immunohistochemically using antibodies raised against PDGF-A, PDGF-B, and PDGFR alpha and beta. Muscles from two dystrophic mouse models (dy and mdx mice) were also immunostained with antibodies raised against PDGFR alpha and beta. In normal human control muscle, neuromuscular junctions and vessels were positively stained with antibodies against PDGF-A, PDGF-B, PDGFR alpha and PDGFR beta. In human dystrophic muscles, PDGF-A, PDGF-B, PDGFR alpha and PDGFR beta were strongly immunolocalized in regenerating muscle fibres and infiltrating macrophages. PDGFR alpha was also immunolocalized to the muscle fibre sarcolemma and necrotic fibres. The most significant finding in this study was a remarkable overexpression of PDGFR beta and, to a lesser extent, PDGFR alpha in the endomysium of DMD and CMD muscles. PDGFR was also overexpressed in the interstitium of muscles from dystrophic mice, particularly dy mice. Double immunolabelling revealed that activated interstitial fibroblasts were clearly positive for PDGFR alpha and beta. However, DMD and CMD muscles with advanced fibrosis showed very poor reactivity against PDGF and PDGFR. Those findings were confirmed by immunoblotting with PDGFR beta. These findings indicate that PDGF and its receptors are significantly involved in the active stage of tissue destruction and are associated with the initiation or promotion of muscle fibrosis. They also have roles in muscle fibre regeneration and signalling at neuromuscular junctions in both normal and diseased muscle.

Healing responses of skin and muscle in critical illness

OBJECTIVE

Many aspects of the care and underlying pathologies in patients suffering critical illness can detrimentally influence the normal healing processes of skin and soft tissues. Although a great diversity of pathologies exists, some aspects of the diseases and their treatments are common in critically ill patients. We aimed to identify some features, both common and specific, that could influence wound healing and the mechanisms by which they may do so.

DESIGN

In this review, we first outline the biology of normal skin and muscle healing and then explore how critical illness may influence the normal healing cascade.

FINDINGS

The healing of skin and skeletal muscle in critical illness is influenced by both underlying disease processes and the intensive care environment. Local and systemic factors can contribute to impaired healing, with the potential to prolong functional disability and increase the likelihood of wound complications. The frequency and number of soft tissue injuries derived from accidental injury, surgical intervention, and the need for invasive monitoring and therapies in the intensive care unit setting are likely to compromise the innate immunity and potentially further jeopardize the patient's ability to heal. Alterations in coagulation, tissue perfusion, inflammation, immune functioning, metabolism, nutrition, and drug therapies will influence healing responses by modifying the biological responses to tissue disruption. Locally, wound contamination, sepsis, tissue hypoxia, edema, and excessive or prolonged local pressure all have the potential to compromise soft tissue healing. One or more of these factors may be present at any time.

CONCLUSION

The skin and soft tissues are vulnerable to both injury and compromised healing when a patient is critically ill and exposed to a critical care environment. The identification of risk factors may aid in forming and modifying treatment strategies when caring for the critically ill patient with soft tissue injuries.

Peyronie's disease: a review

PURPOSE

We provide a current review of Peyronie's disease.

MATERIALS AND METHODS

We reviewed the world peer reviewed literature on the pathology, pathogenesis, diagnosis and treatment of Peyronie's disease.

RESULTS

The incidence of Peyronie's disease has continuously increased during the last 30 years. However, fewer patients need prosthesis surgery as the sole treatment option because of earlier diagnosis, improved medical therapy, refinement in surgical technique and better understanding of the basic sciences of the disease.

CONCLUSIONS

Currently patients with Peyronie's disease have had improvements in prognosis and experienced an expansion of the available therapeutic options.

Effect of nitric oxide on the differentiation of fibroblasts into myofibroblasts in the Peyronie's fibrotic plaque and in its rat model

The myofibroblast shares phenotypic features of both fibroblasts and smooth muscle cells. It plays a critical role in collagen deposition and wound healing and disappears by apoptosis when the wound is closed. Its abnormal persistence leads to hypertrophic scar formation and other fibrotic conditions. Myofibroblasts are present in the fibrotic plaque of the tunica albuginea (TA) of the penis in men with Peyronie's disease (PD), a localized fibrosis that is accompanied by a spontaneous induction of the inducible nitric oxide synthase (iNOS), also observed in the TGFbeta1-elicited, PD-like lesion in the rat model. iNOS expression counteracts fibrosis, by producing nitric oxide (NO) that reduces collagen deposition in part by neutralization of profibrotic reactive oxygen species. In this study we investigated whether fibroblast differentiation into myofibroblasts is enhanced in the human and rat PD-like plaque and in cultures of human tissue fibroblasts. We also examined whether NO reduces this cell differentiation and collagen synthesis. The myofibroblast content in the fibroblast population was measured by quantitative immunohistochemistry as the ratio between alpha-smooth muscle actin (ASMA; myofibroblast marker) and vimentin (general fibroblast marker) levels. We found that myofibroblast content was considerably increased in the human and TGFbeta1-induced rat plaques as compared to control TA. Inhibition of iNOS activity by chronic administration of L-iminoethyl-L-lysine to rats with TGFbeta1-induced TA lesion increased myofibroblast abundance and collagen I synthesis measured in plaque and TA homogenates from animals injected with a collagen I promoter construct driving the expression of beta-galactosidase. Fibroblast differentiation into myofibroblasts occurred with passage in the cell cultures from the human PD plaque, but was minimal in cultures from the TA. Induction of iNOS in PD and TA cultures with a cytokine cocktail and a NO donor, S-nitroso-N-acetyl penicillamine (SNAP), was detected by immunohistochemistry. Both treatments reduced the total number of cells and the number of ASMA positive cells, whereas only SNAP decreased collagen I immunostaining. These results support the hypotheses that myofibroblasts play a role in the development of the PD plaque and that the antifibrotic effects of NO may be mediated at least in part by the reduction of myofibroblast abundance and lead to a reduction in collagen I synthesis.

Inhibition of muscle differentiation by the novel muscleblind-related protein CHCR

Growth factor withdrawal from proliferating myoblasts induces the expression of muscle-specific genes essential for myogenesis. By suppression subtractive hybridization (SSH), we have cloned a novel human cDNA that encodes a Cys3His zinc finger protein named CHCR (Cys3His CCG1-Required). CHCR is related to Muscleblind (Mbl), a Drosophila melanogaster protein required for terminal muscle differentiation. It also displays sequence similarity to EXP/MBNL, a human Mbl protein that interacts with CUG expansions associated with the degenerative muscular disease, myotonic dystrophy (DM1). This relationship with EXP/MBNL and Mbl suggests that CHCR also functions during muscle differentiation. We have found that CHCR mRNA and protein levels decrease upon differentiation of mouse myoblast cells. Constitutive expression of CHCR in C2C12 cells inhibits the induction of sarcomeric myosin heavy chain (MyHC) upon serum deprivation. Induction of myogenin, an earlier marker of muscle differentiation, is inhibited to a lesser extent, while expression of the cell cycle inhibitor, p21, remains unaffected. Loss of CHCR function by morpholino antisense oligonucleotide treatment accelerates MyHC induction during differentiation of myoblast cells. These complementary gain- and loss-of-function results suggest that CHCR is an inhibitor of myogenesis. CHCR represents the first muscleblind-related protein that antagonizes, instead of promotes, muscle differentiation.

Gene expression in Peyronie's disease

Currently, surgical intervention is the only efficacious treatment for Peyronie's disease (PD), a fibromatosis of the tunica albuginea of the penis. Therapies based on the molecular pathways for this disease could provide alternatives to surgical treatment but only recently has the pathophysiology of the Peyronie's disease plaque been investigated at the molecular level. In this review, we examine the current knowledge of gene expression in the PD plaque and the relationship of PD with other fibrotic conditions such as Dupytren's disease. TGFbeta1, along with other growth factors, pro-fibrotic genes, and collagen, are expressed in fibroblasts and myofibroblasts. Myofibroblasts are normally involved in wound contracture and largely eliminated via apoptosis during the late stages of wound remodeling. In the PD plaque, however, these cells persist and may play an important role in the PD plaque fibrosis. The expression levels of TGFbeta1 and pro- and anti-fibrotic gene products, along with the nitric oxide/reactive oxygen species (NO/ROS) ratio in the tunica albuginea, appear to be essential for the formation and progression of the PD plaque and effect the expression of multiple genes. This can be assessed with the recently developed DNA-based chip arrays and results with the PD plaque have been encouraging. OSF-1 (osteoblast recruitment), MCP-1 (macrophage recruitment), procollagenase IV (collagenase degradation), and other fibrotic genes have been identified as being possible candidate regulatory genes. Finally, possible therapeutic avenues for gene-based therapy in the treatment of PD are discussed that may eventually reduce the need for surgical intervention.

Gastrointestinal stem cells

Turnover of the epithelial cell lineages within the gastrointestinal tract is a constant process, occurring every 2-7 days under normal homeostasis and increasing after damage. This process is regulated by multipotent stem cells, which give rise to all gastrointestinal epithelial cell lineages and can regenerate whole intestinal crypts and gastric glands. The stem cells of the gastrointestinal tract are as yet undefined, although it is generally agreed that they are located within a 'niche' in the intestinal crypts and gastric glands. Studies of allophenic tetraparental chimeric mice and targeted stem cell mutations suggest that a single stem cell undergoes asymmetrical division to produce an identical daughter cell, and thus replicate itself, and a committed progenitor cell which further differentiates into an adult epithelial cell type. The discovery of stem cell plasticity in many tissues, including the ability of transplanted bone marrow to transdifferentiate into intestinal subepithelial myofibroblasts, provides a potential use of bone marrow cells to deliver therapeutic genes to damaged tissues, for example, in treatment of mesenchymal diseases in the gastrointestinal tract, such as fibrosis and Crohn's disease. Studies are beginning to identify the molecular pathways that regulate stem cell proliferation and differentiation into adult gastrointestinal cell lineages, such as the Wnt and Notch/Delta signalling pathways, and the importance of mesenchymal-epithelial interactions in normal gastrointestinal epithelium and in development and disease.

Myofibroblasts and mechano-regulation of connective tissue remodelling

During the past 20 years, it has become generally accepted that the modulation of fibroblastic cells towards the myofibroblastic phenotype, with acquisition of specialized contractile features, is essential for connective-tissue remodelling during normal and pathological wound healing. Yet the myofibroblast still remains one of the most enigmatic of cells, not least owing to its transient appearance in association with connective-tissue injury and to the difficulties in establishing its role in the production of tissue contracture. It is clear that our understanding of the myofibroblast its origins, functions and molecular regulation will have a profound influence on the future effectiveness not only of tissue engineering but also of regenerative medicine generally.

The role of stem cells in skeletal and cardiac muscle repair

In postnatal muscle, skeletal muscle precursors (myoblasts) can be derived from satellite cells (reserve cells located on the surface of mature myofibers) or from cells lying beyond the myofiber, e.g., interstitial connective tissue or bone marrow. Both of these classes of cells may have stem cell properties. In addition, the heretical idea that post-mitotic myonuclei lying within mature myofibers might be able to re-form myoblasts or stem cells is examined and related to recent observations for similar post-mitotic cardiomyocytes. In adult hearts (which previously were not considered capable of repair), the role of replicating endogenous cardiomyocytes and the recruitment of other (stem) cells into cardiomyocytes for new cardiac muscle formation has recently attracted much attention. The relative contribution of these various sources of precursor cells in postnatal muscles and the factors that may enhance stem cell participation in the formation of new skeletal and cardiac muscle in vivo are the focus of this review. We concluded that, although many endogenous cell types can be converted to skeletal muscle, the contribution of non-myogenic cells to the formation of new postnatal skeletal muscle in vivo appears to be negligible. Whether the recruitment of such cells to the myogenic lineage can be significantly enhanced by specific inducers and the appropriate microenvironment is a current topic of intense interest. However, dermal fibroblasts appear promising as a realistic alternative source of exogenous myoblasts for transplantation purposes. For heart muscle, experiments showing the participation of bone marrow-derived stem cells and endothelial cells in the repair of damaged cardiac muscle are encouraging.

Gene expression profiles in the Peyronie's disease plaque

OBJECTIVES

To provide molecular insight into the pathophysiology of Peyronie's disease (PD), a preliminary profile of differential gene expression between the PD plaque and control tunica albuginea was obtained with DNA microarrays.

METHODS

Seven PD plaques and five control tunica albugineas were studied. cDNA specimens were prepared from RNA isolated from one calcified PD plaque and one control tissue and hybridized with the Clontech Atlas 1.2 Array. Another set of plaque and control RNA samples was hybridized with the Affymetrix GeneChip. Relative changes of greater than 2.0 defined up-regulation and down-regulation, respectively. RNA from the remaining tissues was used to determine, by reverse transcriptase-polymerase chain reaction and Western blot analysis, the expression of selected individual genes.

RESULTS

Some of up-regulated genes in the PD plaque detected by the Clontech assay were pleiotrophin, monocyte chemotactic protein 1, and early growth response protein, which are involved in osteoblast recruitment, inflammation, and fibroblast proliferation, respectively. Ubiquitin and Id-2, which are involved in tissue remodeling, were down-regulated. The Affymetrix DNA chips identified the up-regulation of elastase (involved in elastic fiber degradation) and the myofibroblast markers alpha and gamma-smooth muscle actin, desmin, and others, as well as the down-regulation of collagenase IV and transforming growth factor-beta modulators. Four of the five genes selected for reverse transcriptase-polymerase chain reaction and Western blotting confirmed the DNA microarray results.

CONCLUSIONS

In the PD tissue, the genes involved in collagen synthesis, myofibroblast differentiation, tissue remodeling, inflammation, ossification, and proteolysis are up-regulated, and the genes that inhibit some of these processes and collagenase are down-regulated.