Smad7 is a TGF-beta-inducible attenuator of Smad2/3-mediated inhibition of embryonic lung morphogenesis

Natural saponins and macrophage polarization: Mechanistic insights and therapeutic perspectives in disease management

Macrophage polarization plays a pivotal role in immune homeostasis and disease progression across inflammatory, neoplastic, and metabolic disorders. Saponins, which are natural compounds with steroidal/triterpenoid structures, demonstrate therapeutic potential through immunomodulatory, anti-inflammatory, and anti-tumor activities. This study aims to highlight the potential of key saponins-such as ginsenosides, astragaloside IV, dioscin, platycodin D, pulsatilla saponins, and panax notoginseng saponins-in modulating macrophage polarization and enhancing conventional therapies, particularly in oncology. We conducted structured searches in PubMed, Google Scholar, and SciFinder (2013-2024) using controlled vocabulary, including "saponins," "macrophage polarization," and "therapeutic effects." Our findings demonstrate that saponins significantly modulate immune responses and improve treatment efficacy. However, clinical translation is hindered by challenges such as poor bioavailability and safety concerns, which limit systemic exposure and therapeutic utility. To overcome these barriers, innovative delivery strategies, including nanoemulsions and engineered exosomes, are essential for enhancing pharmacokinetics and therapeutic index. Future research should prioritize elucidating the molecular mechanisms underlying saponin-mediated macrophage polarization, identifying novel therapeutic targets, and optimizing drug formulations. Addressing these challenges will enable the restoration of immune balance and more effective management of diverse diseases.

LncRNA MBNL1-AS1 represses gastric cancer progression via the TGF-β pathway by modulating miR-424-5p/Smad7 axis

Studies over the past decades have implicated lncRNAs in promoting the development, migration and invasion of gastric cancer (GC). However, the role and mechanism of lncRNA MBNL1-AS1 in GC promotion are poorly understood. In this research, qRT-PCR showed that MBNL1-AS1 was down-regulated in GC tissues and cells. Cell experiments and the animal study demonstrated that MBNL1-AS1 knockdown accelerated GC cell proliferation, migration, and invasion, thus restraining cell apoptosis. Meanwhile, overexpression of MBNL1-AS1 repressed GC cell promotion. Bioinformatics analysis confirmed that MBNL1-AS1 binds to miR-424-5p via negative modulation. Rescue experiments showed that decreased miR-424-5p level inhibited GC cell promotion by silencing MBNL1-AS1. Furthermore, Smad7 was identified as a target of miR-424-5p that could reverse the promotion of GC cell growth mediated by miR-424-5p. Western blot results proved that MBNL1-AS1 affected TGF-β/SMAD pathways by regulating the miR-424-5p/Smad7 axis. Collectively, MBNL1-AS1 restrained GC growth via the miR-424-5p/Smad7 axis and thus could be a promising target for GC therapy. These findings illustrate that lncRNA MBNL1-AS1, as a tumor suppressor gene, participates in GC progression by regulating miR-424-5p/Smad7 axis, thus activating TGF-β/EMT pathways. The evidence may provide a potential marker for GC patients.

Sex-dependent right ventricular hypertrophic gene changes after methamphetamine treatment in mice

Methamphetamine (MA) abuse is associated with the development of pulmonary arterial hypertension (PAH) and subsequent right ventricular failure. A recent clinical study demonstrated that female sex is a major risk factor for MA-induced PAH. The mechanisms associated with increased prevalence and severity of MA-induced PAH in females are still unclear. We hypothesized that MA may promote changes in gene expression in the right ventricle contributing to the development and/or worsening of PAH in females. Male and female C57BL/6 mice were treated with either MA or vehicle. Right and left ventricular systolic pressures (RVSP and LVSP, respectively) were assessed and tissue samples were collected for gene expression and histology. LVSP and RVSP were not affected by MA in either males or females. Right ventricular hypertrophy was significantly increased by MA in females but it was not affected by MA in males. In the female mice, MA-induced right ventricular hypertrophy was associated with increased expression of brain natriuretic peptide gene and members of the TGF-β receptor signaling pathway such as TGF-β receptor-1, smad3 and smad7. In male mice, there were no changes in right ventricular gene expression. Our results suggest that MA caused right ventricular hypertrophy in female mice, but not in males and that this was associated with an increase in hypertrophic genes. The right ventricular hypertrophy was not dependent on increased RVSP suggesting a direct effect of MA on the right ventricle. If this translates to PAH patients, it might explain the poor outcome observed in MA-associated female PAH patients.

Colon epithelial cell TGFβ signaling modulates the expression of tight junction proteins and barrier function in mice

Defective barrier function is a predisposing factor in inflammatory bowel disease (IBD) and colitis-associated cancer (CAC). Although TGFβ signaling defects have been associated with IBD and CAC, few studies have examined the relationship between TGFβ and intestinal barrier function. Here, we examine the role of TGFβ signaling via SMAD4 in modulation of colon barrier function. The Smad4 gene was conditionally deleted in the intestines of adult mice and intestinal permeability assessed using an in vivo 4 kDa FITC-Dextran (FD4) permeability assay. Mouse colon was isolated for gene expression (RNA-sequencing), Western blot, and immunofluorescence analysis. In vitro colon organoid culture was utilized to assess junction-related gene expression by qPCR and transepithelial resistance (TER). In silico analyses of human IBD and colon cancer databases were performed. Mice lacking intestinal expression of Smad4 demonstrate increased colonic permeability to FD4 without gross mucosal damage. mRNA/protein expression analyses demonstrate significant increases in Cldn2/Claudin 2 and Cldn8/Claudin 8, and decreases in Cldn3, Cldn4, and Cldn7/Claudin 7 with intestinal SMAD4 loss in vivo without changes in Claudin protein localization. TGFβ1/BMP2 treatment of polarized SMAD4+ colonoids increases TER. Cldn2, Cldn4, Cldn7, and Cldn8 are regulated by canonical TGFβ signaling, and TGFβ-dependent regulation of these genes is dependent on nascent RNA transcription (Cldn2, Cldn4, Cldn8) but not nascent protein translation (Cldn4, Cldn8). Human IBD/colon cancer specimens demonstrate decreased SMAD4, CLDN4, CLDN7, and CLDN8 and increased CLDN2 compared with healthy controls. Canonical TGFβ signaling modulates the expression of tight junction proteins and barrier function in mouse colon.NEW & NOTEWORTHY We demonstrate that canonical TGFβ family signaling modulates the expression of critical tight junction proteins in colon epithelial cells, and that expression of these tight junction proteins is associated with maintenance of colon epithelial barrier function in mice.

Protective Activity and Underlying Mechanism of Ginseng Seeds against UVB-Induced Damage in Human Fibroblasts

Ginseng seeds are rich in phytosterols, ginsenosides, and fatty acids, and can therefore be used in skincare to delay the aging process. Ginseng seed embryo (GSE) and ginseng seed coat (GSC) were separated from ginseng seeds (Panax ginseng Meyer). This study evaluated the protective activity and underlying mechanism of GSE and GSC on UVB irradiation-induced skin photoaging using Hs68 cells. Their bioactive compounds, including phytosterols, ginsenosides, tocopherols, tocotrienols, and fatty acids were determined by HPLC and GC. The levels of reactive oxygen species, matrix metalloproteinases (MMPs), and collagen levels were measured in human dermal fibroblast cell line, Hs68 cells. The antioxidant capacity and contents of total polyphenols and flavonoids were higher in GSC than those in GSE. Linoleic acid was the major fatty acid in both GSE and GSC. GSE and GSC treatment alleviated UVB-induced increase of reactive oxygen species (ROS), matrix metalloproteinase (MMP)-1, and MMP-3, resulting in reduced collagen degradation. Increased UVB-mediated phosphorylation of mitogen activated protein kinase (MAPK) and activator protein-1 (AP-1) was inhibited by GSE and GSC treatment. Moreover, GSE and GSC effectively upregulated transforming growth factor-β (TGF-β) 1 levels. It was found that ginseng seeds regulate the expression of TGF-β/Smad and MAPK/AP-1 pathways. Ginseng seeds contain various bioactive compounds and have protective activity against UVB-induced skin photoaging. Therefore, ginseng seeds have the potential for use in cosmeceutical preparations.

Bleomycin: A novel osteogenesis inhibitor of dental follicle cells via a TGF-β1/SMAD7/RUNX2 pathway

BACKGROUND AND PURPOSE

Tooth eruption is a complicated process regulated by the dental follicles (DF). Our recent study discovered that tooth eruption was inhibited upon injection of bleomycin into DF. However, the mechanisms were unknown.

EXPERIMENTAL APPROACH

Human dental follicle cells (hDFCs) were treated by bleomycin or exogenous TGF-β1 or transfected by plasmids loading SMAD7 or shRNA targeting SMAD7, followed by osteogenesis induction assay and signalling analysis. Human fresh DF tissues and Wistar rats were used to further confirm bleomycin function.

KEY RESULTS

Bleomycin decreased expression of RUNX2 and osteogenic genes in hDFCs, reducing osteogenic capacity. TGF-β1 expression was up-regulated in bleomycin-treated hDFCs. The effects of exogenous TGF-β1 were similar to those of bleomycin in hDFCs. Additionally, compared to SMAD2/3, SMAD7 expression increased more in bleomycin- or TGF-β1-treated hDFCs. Overexpression of SMAD7 likewise significantly decreased RUNX2 expression and osteogenic capacity of hDFCs. Knockdown of SMAD7 markedly attenuated the inhibitory effects of bleomycin and TGF-β1 on osteogenic capacity and RUNX2 expression of hDFCs. Most importantly, changes in TGF-β1, SMAD7, and RUNX2 expressions were similar in the DF of rats and humans treated with bleomycin.

CONCLUSION AND IMPLICATIONS

SMAD7 was a negative regulator of osteogenic differentiation in DFCs through suppressing RUNX2 expression. Bleomycin or TGF-β1 inhibited osteogenic differentiation of DFCs via a TGF-β1/SMAD7/RUNX2 pathway. Our findings might be beneficial for enhancing the osteogenic activity of DFCs or inhibiting the eruption of undesirable teeth.

Pro- and Anti-fibrogenic Functions of Gram-Negative Bacterial Lipopolysaccharide in the Liver

Extensive research performed over several decades has identified cells participating in the initiation and progression of fibrosis, and the numerous underlying inter- and intra-cellular signaling pathways. However, liver fibrosis continues to be a major clinical challenge as the precise targets of treatment are still elusive. Activation of physiologically quiescent perisinusoidal hepatic stellate cells (HSCs) to a myofibroblastic proliferating, contractile and fibrogenic phenotype is a critical event in the pathogenesis of chronic liver disease. Thus, elucidation of the mechanisms of the reversal to quiescence or inhibition of activated HSCs, and/or their elimination via apoptosis has been the focus of intense investigation. Lipopolysaccharide (LPS), a gut-resident Gram-negative bacterial endotoxin, is a powerful pro-inflammatory molecule implicated in hepatic injury, inflammation and fibrosis. In both acute and chronic liver injury, portal venous levels of LPS are elevated due to increased intestinal permeability. LPS, via CD14 and Toll-like receptor 4 (TLR4) and its adapter molecules, stimulates macrophages, neutrophils and several other cell types to produce inflammatory mediators as well as factors that can activate HSCs and stimulate their fibrogenic activity. LPS also stimulates synthesis of pro- and anti-inflammatory cytokines/chemokines, growth mediators and molecules of immune regulation by HSCs. However, LPS was found to arrest proliferation of activated HSCs and to convert them into non-fibrogenic phenotype. Interestingly, LPS can elicit responses in HSCs independent of CD14 and TLR4. Identifying and/or developing non-inflammatory but anti-fibrogenic mimetics of LPS could be relevant for treating liver fibrosis.

Chitinase 1 regulates pulmonary fibrosis by modulating TGF-β/SMAD7 pathway via TGFBRAP1 and FOXO3

TGF-β1 is a critical mediator of tissue fibrosis in health and disease whose effects are augmented by chitinase 1 (CHIT1). However, the mechanisms that CHIT1 uses to regulate TGF-β1-mediated fibrotic responses have not been defined. Here, we demonstrate that CHIT1 enhances TGF-β1-stimulated fibrotic cellular and tissue responses and TGF-β1 signaling. Importantly, we also demonstrate that these effects are mediated by the ability of CHIT1 to inhibit TGF-β1 induction of its feedback inhibitor, SMAD7. CHIT1 also interacted with TGF-β receptor associated protein 1 (TGFBRAP1) and forkhead box O3 (FOXO3) with TGFBRAP1 playing a critical role in CHIT1 enhancement of TGF-β1 signaling and effector responses and FOXO3 playing a critical role in TGF-β1 induction of SMAD7. These pathways were disease relevant because the levels of CHIT1 were increased and inversely correlated with SMAD7 in tissues from patients with idiopathic pulmonary fibrosis or scleroderma-associated interstitial lung disease. These studies demonstrate that CHIT1 regulates TGF-β1/SMAD7 axis via TGFBRAP1 and FOXO3 and highlight the importance of these pathways in the pathogenesis of pulmonary fibrosis.

Effect of canonical NF-κB signaling pathway on the differentiation of rat dental epithelial stem cells

BACKGROUND

Nuclear factor-κB (NF-κB), an important transcription factor, participates in many physiological and pathological processes such as growth, differentiation, organogenesis, apoptosis, inflammation, and immune response, including tooth development. However, it is still unknown whether NF-κB participates in the regulation of dental epithelial stem cells (DESCs) in postnatal rat incisors. Here, we investigated the specific differentiation regulatory mechanisms of the canonical NF-κB signaling pathway in DESCs and provided the mechanism of cross-talk involved in DESC differentiation.

METHODS

After adding the activator or inhibitor of the NF-κB signaling pathway, Western blot and quantitative real-time PCR were used to analyze the expressions of amelogenesis-related genes and proteins and canonical transforming growth factor-β (TGF-β) signaling. In addition, we used amelogenesis induction in vitro by adding the activator or inhibitor of the NF-κB signaling pathway to the amelogenesis-induction medium, respectively. Recombinant TGF-β was used to activate the TGF-β pathway, and SMAD7 siRNA was used to downregulate the expression of SMAD7 in DESCs.

RESULTS

We found that the expression of amelogenesis-related genes and proteins as well as TGF-β signaling were downregulated, while SMAD7 expression was increased in NF-κB-activated DESCs. In addition, NF-κB-inhibited DESCs exhibited opposite results compared with NF-κB-activated DESCs. Furthermore, the canonical NF-κB signaling pathway suppressed the canonical TGF-β-SMAD signaling by inducing SMAD7 expression involved in the regulation of DESC differentiation.

CONCLUSIONS

These results indicate that the canonical NF-κB signaling pathway participated in the regulation of DESC differentiation, which was through upregulating SMAD7 expression and further suppressing the canonical TGF-β-SMAD signaling pathway.

Gentisic acid prevents the transition from pressure overload-induced cardiac hypertrophy to heart failure

We previously reported that gentisic acid attenuates cardiac hypertrophy and fibrosis in transverse aortic constriction (TAC)-induced cardiac hypertrophy. Here, we examined whether gentisic acid prevents the development of heart failure. Heart failure was induced in mice via chronic TAC. Mice were administered the vehicle, gentisic acid (10 and 100 mg∙kg^-1∙day^-1), or bisoprolol (0.5 mg∙kg^-1∙day^-1) orally for 3 weeks, beginning 3 weeks after TAC. After oral administration of gentisic acid (2000 mg∙kg^-1), no significant differences in organ weight, histology, or analyzed serum and hematological parameters were observed between female mice in the control and gentisic acid-treated groups. Gentisic acid administration inhibited cardiac dysfunction in a dose-dependent manner, and reduced cardiac hypertrophy and fibrosis, as was revealed via western blotting, quantitative real-time PCR, and Masson's trichrome staining. Gentisic acid dose-dependently reduced the expression of fibrosis marker genes, suppressed the renin-angiotensin-aldosterone system, and reduced lung size and pulmonary vascular remodeling. Our data indicate that gentisic acid prevents cardiac hypertrophy, fibrosis, cardiac dysfunction, and pulmonary pathology in TAC-induced heart failure. These findings suggest that supplementation with gentisic acid may provide an advantage in preventing the progression from cardiac hypertrophy to heart failure.

TH17 cell plasticity: The role of dendritic cells and molecular mechanisms

Upon interaction with dendritic cells (DCs), naïve CD4 T cells differentiate into distinct subsets and orchestrate the development of a physiological immune response. When uncontrolled by cellular and molecular mechanisms, CD4 T cells can also lead to immune mediated inflammatory diseases (IMIDs). Initially, these distinct CD4 T-cell subsets were defined according to the expression of a limited number of cytokines. Later it was revealed that CD4 T cells can acquire much more complex functional phenotypes than previously thought. Experimental data showed that the CD4 T-cell subset T_H17 can secrete IFN-γ and IL-4, which are signature molecules of other T-cell subsets. Furthermore, some T_H17 cells can also explore an anti-inflammatory fate and participate in the resolution of the immune response. A more flexible theory has therefore evolved with the scope to better represent the plastic biology of CD4 T cells. In this context, several aspects still remain unclear. The goal of this review is to discuss the role of extrinsic and intrinsic cellular and molecular mechanisms, which can drive the plasticity of T_H17 cells. In particular, we will outline the role of DCs and the function of transcriptional factors in shaping the fate of T_H17 cells towards either a pathogenic or a regulatory phenotype. Finally, we will discuss whether T_H17 cell plasticity could be a target for new therapies for IMIDs. We indeed envision that when the cellular and molecular mechanisms controlling T_H17 plasticity are known, new therapies, which aim to reset the immune system, will be developed. This will be achieved by either selectively depleting only the pathogenic T_H17 cells or, if possible, re converting these cells from pathogenic to regulatory. This will overcome the challenge posed by the immune suppressive side effects caused by the current therapies, which impair the function of CD4 cells or delete all of them, to the detriment of the patient.

MiR-21/Smad 7 signaling determines TGF-β1-induced CAF formation

How TGF-β1-mediated signaling pathways are finely tuned to orchestrate the generation of carcinoma-associated fibroblasts (CAFs) is poorly understood. Here, we demonstrate that miR-21 and the signaling of its target Smad 7 determine TGF-β1-induced CAF formation. In primary cultured fibroblasts, mature miR-21 increases after TGF-β1 treatment, whereas the Smad 7 protein level decreases. MiR-21 binds to the 3′ UTR of Smad7 mRNA and inhibits its translation, rather than causing its degradation. Most importantly, Smad 7 is bound to Smad 2 and 3, which are thought to competitively bind to TGFBR1, and prevents their activation upon TGF-β1 stimulation. The depletion of miR-21 or the overexpression of Smad 7 blocks TGF-β1-induced CAF formation, whereas the overexpression of miR-21 or the depletion of Smad 7 promotes CAF formation, even without TGF-β1 stimulation. Collectively, these findings clearly demonstrate that miR-21 and Smad7 are critical regulators of TGF-β1 signaling during the induction of CAF formation.

Regulatory interactions between androgens, Hoxb5, and TGF β signaling in murine lung development

Androgens enhance airway branching but delay alveolar maturation contributing to increased respiratory morbidity in prematurely born male infants. Hoxb5 protein positively regulates airway branching in developing lung. In other organs, androgen regulation intersects with Hox proteins and TGFβ-SMAD signaling, but these interactions have not been studied in the lung. We hypothesized that androgen alteration of airway branching early in lung development requires Hoxb5 expression and that these androgen-Hoxb5 interactions occur partially through regional changes in TGFβ signaling. To evaluate acute effects of androgen and TGFβ on Hoxb5, E11 whole fetal mouse lungs were cultured with dihydrotestosterone (DHT) with/without Hoxb5 siRNA or TGFβ inhibitory antibody. Chronic in utero DHT exposure was accomplished by exposing pregnant mice to DHT (subcutaneous pellet) from E11 to E18. DHT's ability to enhance airway branching and alter phosphorylated SMAD2 cellular localization was partially dependent on Hoxb5. Hoxb5 inhibition also changed the cellular distribution of SMAD7 protein. Chronic in utero DHT increased Hoxb5 and altered SMAD7 mesenchymal localization. TGFβ inhibition enhanced airway branching, and Hoxb5 protein cellular localization was more diffuse. We conclude that DHT controls lung airway development partially through modulation of Hoxb5 protein expression and that this level of regulation involves interactions with TGFβ signaling.

Myostatin inhibits proliferation but not differentiation of trout myoblasts

The muscle growth in mammals is regulated by several growth factors including myostatin (MSTN), a member of the transforming growth factor-beta (TGF-beta) superfamily. To date, it is unknown in fish whether MSTN could have any effect on proliferation or differentiation of myogenic cells. Using culture of trout satellite cells, we showed that mstn1a and mstn1b mRNA are expressed in myoblasts and that their expression decreased in differentiating myoblasts. We also demonstrated that a treatment with huMSTN decreased the proliferation of IGF1-stimulated myoblasts in a dose-dependent manner. By contrast, treatment of myoblasts with 100 nM of huMSTN for three days, did not affect the percentage of positive cells for myogenin neither the percentage of nuclei in myosin positive cells. Moreover, our results clearly indicated that huMSTN treatment had no effect on MyoD and myogenin protein levels, which suggests that huMSTN did not strongly affect MyoD activity. In conclusion, we showed that huMSTN inhibited proliferation but not differentiation of trout myoblasts, probably resulting from a lack of huMSTN effect on MyoD activity. Altogether, these results show high interspecies differences in the function of MSTN.

Bone morphogenetic protein signalling activity distinguishes histological subsets of paediatric germ cell tumours

Germ cell tumours (GCTs) are cancers of the testis, ovary or extragonadal sites that occur in infants, children and adults. Testicular GCT is the most common cancer in young men aged 15-40 years. Abnormalities in developmental signalling pathways such as wnt/β-catenin, TGF-β/BMP and Hedgehog have been described in many childhood tumours. To date, however, the status of BMP signalling in GCTs has not been described. Herein, we examine BMP-SMAD signalling in a set of clinically-annotated paediatric GCTs. We find that BMP signalling activity is absent in undifferentiated tumours such as seminomas and dysgerminomas, but robustly present in most yolk sac tumours, a differentiated tumour type. Gene expression profiling of TGF-β/BMP pathway genes in germinomas and yolk sac tumours reveals a set of genes that distinguish the two tumour types. There is significant intertumoural heterogeneity between tumours of the same histological subclass, implying that the BMP pathway can be differentially regulated in individual tumours. Finally, through miRNA expression profiling, we identify differential regulation of a set of miRNAs predicted to target the TGF-β/BMP pathway at multiple sites. Taken together, these results suggest that the BMP signalling pathway may represent a new therapeutical target for childhood GCTs.

Atrial fibrillation induces myocardial fibrosis through angiotensin II type 1 receptor-specific Arkadia-mediated downregulation of Smad7

RATIONALE

Tachycardia-induced atrial fibrosis is a hallmark of structural remodeling of atrial fibrillation (AF). The molecular mechanisms underlying the AF-induced atrial fibrosis remain unclear.

OBJECTIVE

To determine the role of angiotensin II (Ang II)/Ang II type 1 (AT(1)) receptor-coupled transforming growth factor (TGF)-β(1)/Smad signaling pathway in the AF-induced atrial fibrosis.

METHODS AND RESULTS

Rapid atrial pacing (1000 ppm) was applied to the left atrium of rabbit heart to induce atrial fibrillation and fibrosis. Quantitative PCR and Western blot analysis revealed that rapid atrial pacing caused a marked increase in the expression of Ang II, TGF-β(1), phosphorylated Smad2/3 (P-Smad2/3), Arkadia, and hydroxyproline synthesis. However, the expression of Smad7, a key endogenous antagonist of the TGF-β(1)/Smad-mediated fibrosis, was significantly decreased. These changes were dose-dependently reversed by AT(1) receptor antagonist losartan, implicating the involvement of AF-induced release of Ang II and activation of AT(1) receptor-specific pathway. In the adult rabbit cardiac fibroblasts, Ang II increased the expression of TGF-β(1), P-Smad2/3, Smad4, Arkadia, and collagen I synthesis and significantly reduced Smad7 expression. These effects of Ang II were reversed by losartan but not by the AT(2) antagonist (PD123319). In addition, extracellular signal-regulated kinase inhibitor and anti-TGF-β(1) antibody also blocked the Ang II-induced downregulation of Smad7. Silencing of Smad7 gene by small interfering RNA abolished the antagonism of losartan on the fibrogenic effects of Ang II on cardiac fibroblasts, whereas overexpression of Smad7 blocked Ang II-induced increase in collagen I synthesis.

CONCLUSIONS

Ang II/AT(1) receptor-specific activation of Arkadia-mediated poly-ubiquitination and degradation of Smad7 may decrease the inhibitory feedback regulation of TGF-β(1)/Smad signaling and serves as a key mechanism for AF-induced atrial fibrosis.

Lung development and implications for hypoplasia found in congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is associated with various degrees of pulmonary hypoplasia and severe persistent pulmonary hypertension in the newborn. These conditions have significant implications for the outcome for the patient. Defects in early lung development are likely to be central to the generation of hypoplasia. A number of mouse models with defects in pathways that are central to lung development were found to have CDH. Understanding all aspects of early lung development will provide fresh insight into the pathogenesis of CDH and its associated conditions.

Regulation of collagen synthesis by inhibitory Smad7 in cardiac myofibroblasts

Transforming growth factor-beta(1) (TGF-beta(1)) signal and downstream Smads play an important role in tissue fibrosis and matrix remodeling in various etiologies of heart failure. Inhibitory Smad7 (I-Smad7) is an inducible regulatory Smad protein that antagonizes TGF-beta(1) signal mediated via direct abrogation of R-Smad phosphorylation. The effect of ectopic I-Smad7 on net collagen production was investigated using hydroxyproline assay. Adenovirus-mediated I-Smad7 gene (at 100 multiplicity of infection) transfer was associated with significant decrease of collagen synthesis in the presence and absence of TGF-beta(1) in primary rat cardiac myofibroblasts. In I-Smad7-infected cells, we also observed the ablation of TGF-beta(1)-induced R-Smad2 phosphorylation vs. LacZ controls. Overdriven I-Smad7 was associated with significantly increased expression of immunoreactive 65-kDa matrix metalloproteinase-2 (MMP-2) protein in culture medium of myofibroblast compared with LacZ-infected cells. Expression of the 72-kDa MMP-2 variant, e.g., the inactive form, was not altered by exogenous I-Smad7 transfection/overexpression. Furthermore, I-Smad7 overexpression was associated with a significant increase and decrease in expression of p27 and phospho-Rb protein, respectively, as well as reduced [(3)H]thymidine incorporation vs. Ad-LacZ-infected controls. We suggest that negative modulation of R-Smad phosphorylation by ectopic I-Smad7 may contribute to the downregulation of collagen in cardiac myofibroblasts and may suppress the proliferation of these cells. Thus treatments targeting the collagen deposition by overexpression of I-Smad7 may provide a new therapeutic strategy for cardiac fibrosis.

Transcriptional control of lung morphogenesis

The vertebrate lung consists of multiple cell types that are derived primarily from endodermal and mesodermal compartments of the early embryo. The process of pulmonary organogenesis requires the generation of precise signaling centers that are linked to transcriptional programs that, in turn, regulate cell numbers, differentiation, and behavior, as branching morphogenesis and alveolarization proceed. This review summarizes knowledge regarding the expression and proposed roles of transcription factors influencing lung formation and function with particular focus on knowledge derived from the study of the mouse. A group of transcription factors active in the endodermally derived cells of the developing lung tubules, including thyroid transcription factor-1 (TTF-1), beta-catenin, Forkhead orthologs (FOX), GATA, SOX, and ETS family members are required for normal lung morphogenesis and function. In contrast, a group of distinct proteins, including FOXF1, POD1, GLI, and HOX family members, play important roles in the developing lung mesenchyme, from which pulmonary vessels and bronchial smooth muscle develop. Lung formation is dependent on reciprocal signaling among cells of both endodermal and mesenchymal compartments that instruct transcriptional processes mediating lung formation and adaptation to breathing after birth.

The role of TGF-beta superfamily during T cell development: new insights

Members of the transforming growth factor beta (TGF-beta) superfamily are soluble factors that regulate a variety of functional responses including proliferation, differentiation, apoptosis and cell cycle, among others, depending not only on the cell type and its differentiation state, but also on the milieu of cytokines present. All three members of this superfamily: TGF-betas, bone morphogenetic proteins (BMPs) and Activins, have been shown to be expressed in the thymus suggesting their potential role as regulators of the T lymphocyte differentiation process. Although initial reports described the role of TGF-beta in controlling specific checkpoints during thymocyte development, recent data has provided new evidence on the role of BMPs and Activins in this process. This review provides new insights on the function of members of the TGF-beta superfamily at different stages of thymocyte development.

ALK-5 mediates endogenous and TGF-beta1-induced expression of connective tissue growth factor in embryonic lung

Transforming growth factor-beta1 (TGF-beta1) has been implicated as a major negative regulator of lung branching morphogenesis. Since connective tissue growth factor (CTGF) is a downstream mediator of TGF-beta1 effects on mesenchymal cells, we hypothesized that TGF-beta1 induces CTGF expression in mouse embryonic lung explants and that CTGF mediates TGF-beta1 inhibition of branching morphogenesis. We show that addition of TGF-beta1 to the serum-free medium of embryonic day (E)12.5 lung explant cultures inhibited branching morphogenesis and induced CTGF mRNA expression in time- and dose-dependent manners. In contrast to basal endogenous CTGF protein, which was exclusively localized in the distal airway epithelium, TGF-beta1-induced CTGF protein was localized in both the epithelium and the mesenchyme. Addition of exogenous CTGF to culture medium directly inhibited branching morphogenesis. To identify the signal transduction pathway through which TGF-beta1 induces CTGF, we used SB431542, a specific inhibitor for TGF-beta type I receptor (TbetaRI)/ALK-5 to block TGF-beta1-induced Smad2/3 phosphorylation. Consequently, SB431542 stimulated normal branching morphogenesis and blocked TGF-beta1 inhibition of branching. Furthermore, SB-431542 blocked both endogenous and TGF-beta1-induced expression of CTGF mRNA and protein. These results demonstrate for the first time that TGF-beta1 induces CTGF expression in mouse embryonic lung explants, that CTGF inhibits branching morphogenesis, and that both endogenous and TGF-beta1-induced CTGF expression are mediated by the TbetaRI/ALK-5-dependent Smad2 signaling pathway.

Antenatal Ureaplasma urealyticum respiratory tract infection stimulates proinflammatory, profibrotic responses in the preterm baboon lung

Chronic inflammation and fibrosis are hallmarks of lung pathology of newborn Ureaplasma infection. We hypothesized that antenatally acquired Ureaplasma stimulates a chronic inflammatory, profibrotic immune response that contributes to lung injury, altered developmental signaling, and fibrosis. Lung specimens from 125-d gestation baboon newborns ventilated for 14 d that were either infected antenatally with Ureaplasma serovar 1 or noninfected, and 125-d and 140-d gestational controls were obtained from the Baboon BPD Resource Center (San Antonio, TX). Trichrome stain to assess fibrosis and immunohistochemistry for alpha-smooth muscle actin (alpha-SMA) and transforming growth factor beta1 (TGFbeta1) were performed. Lung homogenates were analyzed by enzyme-linked immunosorbent assay (ELISA) for cytokines [tumor necrosis factor alpha (TNFalpha), interleukin (IL)-1beta, TGFbeta1, oncostatin M (OSM), IL-10, and interferon gamma (IFNgamma)] and the chemokine MCP-1 and by Western blot for Smad2, Smad3, and Smad7. Compared with noninfected ventilated and gestational controls, Ureaplasma-infected lungs demonstrated more extensive fibrosis, increased alpha-SMA and TGFbeta1 immunostaining, and higher concentrations of active TGFbeta1, IL-1beta, and OSM, but no difference in IL-10 levels. There was a trend toward higher Smad2/Smad7 and Smad3/Smad7 ratios in Ureaplasma lung homogenates, consistent with up-regulation of TGFbeta1 signaling. Collectively, these data suggest that a prolonged proinflammatory response initiated by intrauterine Ureaplasma infection contributes to early fibrosis and altered developmental signaling in the immature lung.

Molecular mechanisms of early lung specification and branching morphogenesis

The "hard wiring" encoded within the genome that determines the emergence of the laryngotracheal groove and subsequently early lung branching morphogenesis is mediated by finely regulated, interactive growth factor signaling mechanisms that determine the automaticity of branching, interbranch length, stereotypy of branching, left-right asymmetry, and finally gas diffusion surface area. The extracellular matrix is an important regulator as well as a target for growth factor signaling in lung branching morphogenesis and alveolarization. Coordination not only of epithelial but also endothelial branching morphogenesis determines bronchial branching and the eventual alveolar-capillary interface. Improved prospects for lung protection, repair, regeneration, and engineering will depend on more detailed understanding of these processes. Herein, we concisely review the functionally integrated morphogenetic signaling network comprising the critical bone morphogenetic protein, fibroblast growth factor, Sonic hedgehog, transforming growth factor-beta, vascular endothelial growth factor, and Wnt signaling pathways that specify and drive early embryonic lung morphogenesis.

Bone morphogenetic protein-7 signals opposing transforming growth factor beta in mesangial cells

Bone morphogenetic protein-7 (BMP7) is expressed in adult kidney and reduces renal fibrogenesis when given exogenously to rodents with experimental chronic nephropathies. In mesangial cells that regulate glomerular fibrosis in vivo, BMP7 inhibits transforming growth factor beta (TGF-beta)-driven fibrogenesis, primarily by preventing the TGF-beta-dependent down-regulation of matrix degradation and up-regulation of PAI-1. The signals and mechanisms of the BMP7 opposition to actions of TGF-beta are unknown. Here we show in mesangial cells that BMP7 reduces nuclear accumulation of Smad3 and blocks the transcriptional up-regulation of the TGF-beta/Smad3 target, CAGA-lux. Smad5 knock-down impairs the ability of BMP7 to interfere with the activation of CAGA-lux and the accumulation of PAI-1 by TGF-beta indicating that Smad5 is required. Smad5 knock-down also reduces the rise in Smad6 upon BMP7. Forced expression of smad5 (found to be the preferred BMP7-induced receptor-activated Smad signal in mesangial cells) or of smad6 mimics BMP7 in opposing the increase in transcriptional activation of PAI-1 and its secretion upon TGF-beta. This suggests a model for the BMP7-induced opposition to TGF-beta-dependent mesangial fibrogenesis requiring Smad5; the model involves the inhibitory Smad6 downstream of Smad5 as well as reduced availability of Smad3 in the nucleus. BMP7 does not require signaling through Erk1/2, p38, or JNK and does not utilize the TGF-beta transcriptional co-repressors Ski or SnoN in mesangial cells. These studies provide first insights into mechanisms through which BMP7 opposes TGF-beta-induced glomerular fibrogenesis.

Advanced glycation end products activate Smad signaling via TGF-beta-dependent and independent mechanisms: implications for diabetic renal and vascular disease

While it is thought that advanced glycation end products (AGEs) act by stimulating transforming growth factor (TGF)-beta to mediate diabetic injury, we report that AGEs can activate TGF-beta signaling, Smads, and mediate diabetic scarring directly and independently of TGF-beta. AGEs activate Smad2/3 in renal and vascular cells at 5 min, peaking over 15-30 min before TGF-beta synthesis at 24 h and occurs in TGF-beta receptor I and II mutant cells. This is mediated by RAGE and ERK/p38 mitogen-activated protein kinases (MAPKs). In addition, AGEs also activate Smads at 24 h via the classic TGF-beta-dependent pathway. A substantial inhibition of AGE-induced Smad activation and collagen synthesis by ERK/p38 MAPK inhibitors, but not by TGF-beta blockade, suggests that the MAPK-Smad signaling crosstalk pathway is a key mechanism in diabetic scarring. Prevention of AGE-induced Smad activation and collagen synthesis by overexpression of Smad7 indicates that Smad signaling may play a critical role in diabetic complications. This is further supported by the findings that activation of Smad2/3 in human diabetic nephropathy and vasculopathy is associated with local deposition of AGEs and up-regulation of RAGE. Thus, AGEs act by activating Smad signaling to mediate diabetic complications via both TGF-beta-dependent and -independent pathways, shedding new light on the pathogenesis of diabetic organ injury.

Growth factor signaling in lung morphogenetic centers: automaticity, stereotypy and symmetry

Lung morphogenesis is stereotypic, both for lobation and for the first several generations of airways, implying mechanistic control by a well conserved, genetically hardwired developmental program. This program is not only directed by transcriptional factors and peptide growth factor signaling, but also co-opts and is modulated by physical forces. Peptide growth factors signal within repeating epithelial-mesenchymal temporospatial patterns that constitute morphogenetic centers, automatically directing millions of repetitive events during both stereotypic branching and nonstereotypic branching as well as alveolar surface expansion phases of lung development. Transduction of peptide growth factor signaling within these centers is finely regulated at multiple levels. These may include ligand expression, proteolytic activation of latent ligand, ligand bioavailability, ligand binding proteins and receptor affinity and presentation, receptor complex assembly and kinase activation, phosphorylation and activation of adapter and messenger protein complexes as well as downstream events and cross-talk both inside and outside the nucleus. Herein we review the critical Sonic Hedgehog, Fibroblast Growth Factor, Bone Morphogenetic Protein, Vascular Endothelial Growth Factor and Transforming Growth Factorbeta signaling pathways and propose how they may be functionally coordinated within compound, highly regulated morphogenetic gradients that drive first stereotypic and then non-stereotypic, automatically repetitive, symmetrical as well as asymmetrical branching events in the lung.

Do different branching epithelia use a conserved developmental mechanism?

Formation of branching epithelial trees from unbranched precursors is a common process in animal organogenesis. In humans, for example, this process gives rise to the airways of the lungs, the urine-collecting ducts of the kidneys and the excretory epithelia of the mammary, prostate and salivary glands. Branching in these different organs, and in different animal classes and phyla, is morphologically similar enough to suggest that they might use a conserved developmental programme, while being dissimilar enough not to make it obviously certain that they do. In this article, I review recent discoveries about the molecular regulation of branching morphogenesis in the best-studied systems, and present evidence for and against the idea of there being a highly conserved mechanism. Overall, I come to the tentative conclusion that key mechanisms are highly conserved, at least within vertebrates, but acknowledge that more work needs to be done before the case is proved beyond reasonable doubt.

Regulation of TGF-beta ligand and receptor expression in neonatal rat lungs exposed to chronic hypoxia

Long-term effects of hypoxia are largely due to its modulatory effects on proliferation and differentiation of epithelial and endothelial cells, processes also regulated by the transforming growth factor (TGF)-beta system. We investigated the effects of hypoxia on the TGF-beta system in rat lungs from different developmental stages. Sprague-Dawley rats were exposed to 9.5% oxygen during either the first 2 wk of life or adulthood. Analysis revealed an arrest of alveolarization in hypoxic postnatal day 14 rats. Bioactive TGF-beta levels in bronchoalveolar lavage fluid were increased in these animals, and Western blot analysis revealed upregulation of TGF-beta receptor (TbetaR) I and II. None of these changes was observed in hypoxic adults. Hypoxia did, however, lead to decreased expression of TbetaRIII in both postnatal day 14 and adult rats. Immunohistochemical analysis localized TbetaRI-III predominantly to bronchiolar and alveolar epithelium; these patterns did not change with hypoxia. Thus we observed changes in TGF-beta activity and TbetaR isotype expression in rat lung that parallel the arrest in alveolarization seen with chronic hypoxia in early development. These alterations may partly explain the morphological changes observed in hypoxia.

Zebrafish Smad7 is regulated by Smad3 and BMP signals

Growth factors of the TGF-beta superfamily such as BMPs and Nodals are important signaling factors during all stages of animal development. Smad proteins, the cytoplasmic mediators of most TGF-beta signals in vertebrates, play central roles not only for transmission but also in controlling inductive TGF-beta signals by feedback regulation. Here, we describe cloning, expression pattern, transcriptional regulation, and functional properties of two novel zebrafish Smad proteins: the TGF-beta agonist Smad3b, and the anti-Smad Smad7. We show that zebrafish Smad3b, in contrast to the related zebrafish Smad2, can induce mesoderm independently of TGF-beta signaling. Although mammalian Smad3 was shown to inhibit expression of the organizer-specific genes goosecoid, zebrafish smad3b activates organizer genes such as goosecoid. Furthermore, we show that Smad3 and BMP signals activate smad7. Because Smad7 blocks distinct TGF-beta signals in early zebrafish development, our data provide hints for new roles of smad3 genes in the regulation and modulation of TGF-beta signals. In summary, our analyses point out differences of Smad3b and Smad2 functions in zebrafish and provide the first link of smad3 and smad7 function in context of vertebrate development.

Smad7 inhibits fibrotic effect of TGF-Beta on renal tubular epithelial cells by blocking Smad2 activation

It has been shown that transforming growth factor-beta (TGF-beta) is a potent mediator in renal fibrosis and that Smad proteins are critical intracellular mediators in TGF-beta signaling. It is here reported that TGF-beta mediates renal fibrogenesis in tubular epithelial cells (TEC) in association with the activation of Smad2 and that overexpression of Smad7 blocks this fibrotic process. Using a normal rat kidney tubular epithelial cell line (NRK52E), it was determined that TGF-beta1 induces Smad2 phosphorylation and nuclear localization in both a dose- and time-dependent manner. The activation of Smad2 was evident at 5 min (20%), peaked at 15 to 30 min (85%), and declined to baseline levels by 2 h (5 to 10%). This was associated with de novo expression of collagens I, III, and IV and the transformation of TEC into a "myofibroblast" phenotype with de novo expression of alpha-smooth muscle actin (alpha-SMA) and with the loss of E-cadherin (>50%). To investigate a negative regulatory role of Smad7 in renal fibrosis, the Smad 7 gene was stably transfected and its expression was tightly controlled by doxycycline into NRK52E cells. Overexpression of Smad7 induced by doxycycline results in marked inhibition of TGF-beta-induced Smad2 activation (90% downward arrow) with the prevention of collagen synthesis and myofibroblast transformation. Thus, Smad2 activation occurs in the fibrogenic response of TEC to TGF-beta, and this process is blocked by overexpression of Smad7. This indicates that Smad signaling is a key pathway of TGF-beta-mediated renal fibrosis and suggests that treatments targeting the inactivation of Smad2 by overexpression of Smad7 may provide a new therapeutic strategy for renal fibrosis.

Receptor-regulated and inhibitory Smads are critical in regulating transforming growth factor beta-mediated Meckel's cartilage development

The proper development of Meckel's cartilage is critical for craniofacial skeletogenesis, because it serves as the primordium for the formation of mandible, malleus, incus, and sphenomandibular ligament. Cranial neural crest (CNC) cells contribute significantly to the formation of Meckel's cartilage. Members of the transforming growth factor beta (TGF-beta) family control the proliferation and differentiation of CNC cells during craniofacial skeletogenesis. TGF-beta signaling is transduced from the cell membrane to the nucleus by means of specific type I and type II receptors and phosphorylated Smad proteins. Here we demonstrate that application of TGF-beta promotes chondrogenesis by specifically increasing proliferation of CNC-derived chondrocytes and production of extracellular matrix. To understand the molecular regulation of TGF-beta signaling, we have examined the biological function of both TGF-beta receptor-regulated and inhibitory Smads during Meckel's cartilage development. The expression patterns of Smad2, 3, and 7 are identical to the ones of endogenous TGF-beta and its cognate receptors during Meckel's cartilage development, establishing the potential that these intracellular signaling Smads may regulate TGF-beta-mediated chondrogenesis. Functional haploinsufficiency of Smad2 delays TGF-beta-mediated Meckel's cartilage development. Overproduction of Smad7 severely inhibits Meckel's cartilage formation, indicating a negative feedback on TGF-beta signaling by inhibitory Smad is critical in orchestrating TGF-beta-mediated gene regulation during embryonic chondrogenesis. The effectiveness of TGF-beta signaling is highly sensitive to the level of Smad gene expression.

Smad7 and Smad6 differentially modulate transforming growth factor beta -induced inhibition of embryonic lung morphogenesis

Transforming growth factors beta (TGF-beta) are known negative regulators of lung development, and excessive TGF-beta production has been noted in pulmonary hypoplasia associated with lung fibrosis. Inhibitory Smad7 was recently identified to antagonize TGF-beta family signaling by interfering with the activation of TGF-beta signal-transducing Smad complexes. To investigate whether Smad7 can regulate TGF-beta-induced inhibition of lung morphogenesis, ectopic overexpression of Smad7 was introduced into embryonic mouse lungs in culture using a recombinant adenovirus containing Smad7 cDNA. Although exogenous TGF-beta efficiently reduced epithelial lung branching morphogenesis in control virus-infected lung culture, TGF-beta-induced branching inhibition was abolished after epithelial transfer of the Smad7 gene into lungs in culture. Smad7 also prevented TGF-beta-mediated down-regulation of surfactant protein C gene expression, a marker of bronchial epithelial differentiation, in cultured embryonic lungs. Moreover, we found that Smad7 transgene expression blocked Smad2 phosphorylation induced by exogenous TGF-beta ligand in lung culture, indicating that Smad7 exerts its inhibitory effect on both lung growth and epithelial cell differentiation through modulation of TGF-beta pathway-restricted Smad activity. However, the above anti-TGF-beta signal transduction effects were not observed in cultured embryonic lungs with Smad6 adenoviral gene transfer, suggesting that Smad7 and Smad6 differentially regulate TGF-beta signaling in developing lungs. Our data therefore provide direct evidence that Smad7, but not Smad6, prevents TGF-beta-mediated inhibition of both lung branching morphogenesis and cytodifferentiation, establishing the mechanistic basis for Smad7 as a novel target to ameliorate aberrant TGF-beta signaling during lung development, injury, and repair.