c-Ski inhibits the proliferation of vascular smooth muscle cells via suppressing Smad3 signaling but stimulating p38 pathway

Association of TGF-β Canonical Signaling-Related Core Genes With Aortic Aneurysms and Aortic Dissections

Transforming growth factor-beta (TGF-β) signaling is essential for the maintenance of the normal structure and function of the aorta. It includes SMAD-dependent canonical pathways and noncanonical signaling pathways. Accumulated genetic evidence has shown that TGF-β canonical signaling-related genes have key roles in aortic aneurysms (AAs) and aortic dissections and many gene mutations have been identified in patients, such as those for transforming growth factor-beta receptor one TGFBR1, TGFBR2, SMAD2, SMAD3, SMAD4, and SMAD6. Aortic specimens from patients with these mutations often show paradoxically enhanced TGF-β signaling. Some hypotheses have been proposed and new AA models in mice have been constructed to reveal new mechanisms, but the role of TGF-β signaling in AAs is controversial. In this review, we focus mainly on the role of canonical signaling-related core genes in diseases of the aorta, as well as recent advances in gene-mutation detection, animal models, and in vitro studies.

Ski regulates proliferation and migration of reactive astrocytes induced by lipopolysaccharide (LPS) through PI3K/Akt pathway

Spinal cord injury (SCI) is a leading cause of disability and death worldwide. Reactive astrogliosis, a typical feature of SCI, undergoes various molecular and morphological changes and contributes to glial scar formation, which impedes axonal regeneration. Ski is a novel molecule that regulates the biological characteristics of astrocytes after spinal cord injury, but its function and the exact mechanism of its overexpression in reactive astrocyte proliferation and migration after SCI remain unclear. The purpose of this study was to elucidate the effect and mechanism of Ski on the proliferation and migration of reactive astrocytes, and to regulate the spatiotemporal formation of glial scars after SCI. In an in vitro lipopolysaccharide (LPS)-induced astrocyte injury model, the expression of Ski was upregulated in a time-dependent manner in LPS-induced astrocytes, and the upregulation of Ski was accompanied by that of PCNA, CDK4, CyclinD1, and other proliferation-related proteins. Our findings suggest that Ski promotes the proliferation and migration of reactive astrocytes. Next, astrocytes were transfected with a specific lentivirus to cause the overexpression of Ski, which significantly enhanced the proliferation and migration of reactive astrocytes and LPS-induced activation of the PI3K/Akt pathway. The PI3K/Akt pathway inhibitor LY294002 significantly inhibited the proliferation and migration of LPS-induced reactive astrocytes after Ski overexpression. In conclusion, Ski regulates LPS-induced astrocyte proliferation and migration through the PI3K/Akt pathway, making Ski a promising target for strategies to combat glial scarring after SCI.

Decreased phosphorylation facilitates the degradation of the endogenous protective molecule c-Ski in vascular smooth muscle cells

The dysfunction of vascular smooth muscle cells (VSMCs) is critical for atherosclerosis (AS) progression. Autophagy is indispensable during phenotypic switching and proliferation of VSMCs, contribute to AS development. Cellular Sloan-Kettering Institute (c-Ski), the repressor of TGF-β signaling, is involved in diverse physiological and pathological processes. We previously defined c-Ski also as an endogenous protective molecule against AS via inhibiting abnormal proliferation and autophagy of VSMCs. However, the endogenous level of c-Ski in VSMCs is markedly decreased during the progression of AS, so that the protective effect is drastically weakened. Elucidating the molecular mechanisms is key to the understanding of AS development and treatment. We determined that oxidized low-density lipoprotein (ox-LDL) and platelet-derived growth factor (PDGF) directly induced the degradation of c-Ski protein, closely associated with reducing its phosphorylation. Serine₃₈₃ (S383) was identified as the crucial phosphorylation site for stabilizing protein expression and nuclear location of c-Ski, which was responsible for its transcriptional suppression of autophagy-related genes. Decreased S383 phosphorylation facilitated nuclear export and degradation of c-Ski, thereby lessened its inhibitory effect on induction of autophagy genes. These findings provide a novel view of c-Ski modification and function modulation under some vascular injury factors, which point to a new potential therapeutic strategy by targeting c-Ski.

Fibroblast mechanosensing, SKI and Hippo signaling and the cardiac fibroblast phenotype: Looking beyond TGF-β

Cardiac fibroblast activation to hyper-synthetic myofibroblasts following a pathological stimulus or in response to a substrate with increased stiffness may be a key tipping point for the evolution of cardiac fibrosis. Cardiac fibrosis per se is associated with progressive loss of heart pump function and is a primary contributor to heart failure. While TGF-β is a common cytokine stimulus associated with fibroblast activation, a druggable target to quell this driver of fibrosis has remained an elusive therapeutic goal due to its ubiquitous use by different cell types and also in the signaling complexity associated with SMADs and other effector pathways. More recently, mechanical stimulus of fibroblastic cells has been revealed as a major point of activation; this includes cardiac fibroblasts. Further, the complexity of TGF-β signaling has been offset by the discovery of members of the SKI family of proteins and their inherent anti-fibrotic properties. In this respect, SKI is a protein that may bind a number of TGF-β associated proteins including SMADs, as well as signaling proteins from other pathways, including Hippo. As SKI is also known to directly deactivate cardiac myofibroblasts to fibroblasts, this mode of action is a putative candidate for further study into the amelioration of cardiac fibrosis. Herein we provide a synthesis of this topic and highlight novel candidate pathways to explore in the treatment of cardiac fibrosis.

Genetic Insights Into Smooth Muscle Cell Contributions to Coronary Artery Disease

Coronary artery disease is a complex cardiovascular disease involving an interplay of genetic and environmental influences over a lifetime. Although considerable progress has been made in understanding lifestyle risk factors, genetic factors identified from genome-wide association studies may capture additional hidden risk undetected by traditional clinical tests. These genetic discoveries have highlighted many candidate genes and pathways dysregulated in the vessel wall, including those involving smooth muscle cell phenotypic modulation and injury responses. Here, we summarize experimental evidence for a few genome-wide significant loci supporting their roles in smooth muscle cell biology and disease. We also discuss molecular quantitative trait locus mapping as a powerful discovery and fine-mapping approach applied to smooth muscle cell and coronary artery disease-relevant tissues. We emphasize the critical need for alternative genetic strategies, including cis/trans-regulatory network analysis, genome editing, and perturbations, as well as single-cell sequencing in smooth muscle cell tissues and model organisms, under both normal and disease states. By integrating multiple experimental and analytical modalities, these multidimensional datasets should improve the interpretation of coronary artery disease genome-wide association studies and molecular quantitative trait locus signals and inform candidate targets for therapeutic intervention or risk prediction.

Knockdown of Ski decreases osteosarcoma cell proliferation and migration by suppressing the PI3K/Akt signaling pathway

Ski, an evolutionary conserved protein, is involved in the development of a number of tumors, such as Barrett's esophagus, leukemia, colorectal cancer, gastric cancer, pancreatic cancer, hemangiomas and melanoma. However, studies on the functions of Ski in osteosarcoma (OS) are limited. In this study, firstly the differential expression of Ski in OS tissues and osteochondroma tissues was detected, and the expression of Ski in both human OS cell lines (MG63 and U2OS) and normal osteoblasts (hFoB1.19) was then detected. The results demonstrated that Ski expression was significantly upregulated in both human OS tissues and cell lines. The results led us to hypothesize that Ski may play an essential role in the pathological process of OS. Thus, Ski specific small interfere RNA (Ski-siRNA) was used. The results revealed that OS cell proliferation was markedly inhibited following the knockdown of Ski, which was identified by CCK8 assay, EdU staining and cell cycle analysis. In addition, OS cell migration was significantly suppressed following Ski knockdown, which was identified by wound healing assay. Moreover, the protein levels of p-PI3K and p-Akt in OS cells declined prominently following Ski knockdown. On the whole, the findings of this study revealed that Ski expression was significantly upregulated in OS tissue and OS cells. The knockdown of Ski decreased OS cell proliferation and migration, which was mediated by blocking the PI3K/Akt signaling pathway. Thus, Ski may act as a tumor promoter gene in tumorigenesis, and Ski may prove to be a potential therapeutic target for the treatment of OS.

Glucocorticoid Enhanced the Expression of Ski in Osteonecrosis of Femoral Head: The Effect on Adipogenesis of Rabbit BMSCs

Glucocorticoid (GC)-induced osteonecrosis has been considered as the most serious side effect in long-term or over-dose steroid therapy. The decreased bone mass and increased marrow fat tissue demonstrated that GC can destroy the normal differentiation of bone marrow mesenchymal stem cells (BMSCs), which accelerates adipogenesis but not osteogenesis. However, the underlying mechanisms are still unclear. Ski, an evolutionary conserved protein, is a multifunctional transcriptional regulator that involved in regulating signaling pathways associated with adipogenesis differentiation, but the concrete function remains unclear. In this work, we first established a methylprednisolone (MPS)-induced osteonecrosis of femoral head (ONFH) rabbit model, in which the expression of Ski, PPAR-γ, and FABP4 was up-regulated compared with control group, and then we induced the isolated BMSCs from rabbit with dexamethasone (Dex) in vitro and the results showed that the Ski expression was up-regulated by Dex in a dose- and time-dependent manner. Therefore, we demonstrated that the expression of Ski was up-regulated in glucocorticoid-related osteonecrosis disease in vivo and in vitro. Moreover, the adipogenesis differentiation capacity of BMSCs was enhanced after induced by Dex, which was identified by Oil Red O staining, and the up-regulated PPAR-γ and FABP4 expression. To further study the function of Ski in BMSC after induced by Dex, Ski specific small interfering RNA (Ski-siRNA) was used. Results showed that knockdown of Ski obviously decreased adipogenesis differentiation evident by Oil Red O staining, and the expression of PPAR-γ and FABP4 was down-regulated simultaneously. Collectively, our findings suggest that Ski increased significantly during glucocorticoid-induced adipogenic differentiation of BMSCs, and the expression level was consistent with adipogenic-related proteins including PPAR-γ and FABP4. Based on the above data, we believe that Ski might become a new molecule in the treatment of GC-induced ONFH and our study could provide a basis for further study on the detailed function of Ski in ONFH.

Spatio-Temporal Expression and Functional Analysis of miR-206 in Developing Orofacial Tissue

BACKGROUND

Development of the mammalian palate is dependent on precise, spatiotemporal expression of a panoply of genes. MicroRNAs (miRNAs), the largest family of noncoding RNAs, function as crucial modulators of cell and tissue differentiation, regulating expression of key downstream genes.

OBSERVATIONS

Our laboratory has previously identified several developmentally regulated miRNAs, including miR-206, during critical stages of palatal morphogenesis. The current study reports spatiotemporal distribution of miR-206 during development of the murine secondary palate (gestational days 12.5-14.5).

RESULT AND CONCLUSION

Potential cellular functions and downstream gene targets of miR-206 were investigated using functional assays and expression profiling, respectively. Functional analyses highlighted potential roles of miR-206 in governing TGFß- and Wnt signaling in mesenchymal cells of the developing secondary palate. In addition, altered expression of miR-206 within developing palatal tissue of TGFß3-/- fetuses reinforced the premise that crosstalk between this miRNA and TGFß3 is crucial for secondary palate development.

Transcriptional cofactors Ski and SnoN are major regulators of the TGF-β/Smad signaling pathway in health and disease

The transforming growth factor-β (TGF-β) family plays major pleiotropic roles by regulating many physiological processes in development and tissue homeostasis. The TGF-β signaling pathway outcome relies on the control of the spatial and temporal expression of >500 genes, which depend on the functions of the Smad protein along with those of diverse modulators of this signaling pathway, such as transcriptional factors and cofactors. Ski (Sloan-Kettering Institute) and SnoN (Ski novel) are Smad-interacting proteins that negatively regulate the TGF-β signaling pathway by disrupting the formation of R-Smad/Smad4 complexes, as well as by inhibiting Smad association with the p300/CBP coactivators. The Ski and SnoN transcriptional cofactors recruit diverse corepressors and histone deacetylases to repress gene transcription. The TGF-β/Smad pathway and coregulators Ski and SnoN clearly regulate each other through several positive and negative feedback mechanisms. Thus, these cross-regulatory processes finely modify the TGF-β signaling outcome as they control the magnitude and duration of the TGF-β signals. As a result, any alteration in these regulatory mechanisms may lead to disease development. Therefore, the design of targeted therapies to exert tight control of the levels of negative modulators of the TGF-β pathway, such as Ski and SnoN, is critical to restore cell homeostasis under the specific pathological conditions in which these cofactors are deregulated, such as fibrosis and cancer.

Proteins that repress molecular signaling through the transforming growth factor-beta (TGF-β) pathway offer promising targets for treating cancer and fibrosis. Marina Macías-Silva and colleagues from the National Autonomous University of Mexico in Mexico City review the ways in which a pair of proteins, called Ski and SnoN, interact with downstream mediators of TGF-β to inhibit the effects of this master growth factor. Aberrant levels of Ski and SnoN have been linked to diverse range of diseases involving cell proliferation run amok, and therapies that regulate the expression of these proteins could help normalize TGF-β signaling to healthier physiological levels. For decades, drug companies have tried to target the TGF-β pathway, with limited success. Altering the activity of these repressors instead could provide a roundabout way of remedying pathogenic TGF-β activity in fibrosis and oncology.

Spatiotemporal expression of Ski after rat spinal cord injury

Ski is an evolutionarily conserved protein and widely participates in the regulation of various pathological and physiological processes such as wound healing, liver regeneration, development of the embryonic nervous system, muscle differentiation, and progression of many kinds of tumors. However, the distribution and function of Ski in central nervous system lesion and disease remain unclear. In this study, we investigated the spatiotemporal expression of Ski in a spinal cord injury (SCI) model in adult rats. Western Blot analysis indicated that Ski was expressed in both normal and injured spinal cord, and showed a significant upregulation after SCI compared with the sham group. Double-labeled immunofluorescence staining showed that Ski was significantly expressed in astrocytes, but not in the neurons. Western Blot analyses of glial fibrillary acidic protein (GFAP) and BBB scores were carried out and correlation analysis showed a positive correlation between them. In addition, the relative expression level of Ski was also positively correlated with the relative expression level of GFAP. Moreover, the conspicuous co-expression band of Ski and GFAP at the lesion border was found in the results of immunofluorescence staining combined with the pattern of glial scar formation reflected by H&E staining; in addition, it was found that Ski was also highly associated with glial scar. On the basis of our data, we speculated that Ski might play an important role in the process of reactive astrogliosis after SCI and our study might provide a basis for further study on the detailed role of Ski in astrocytes.

Function, Role, and Clinical Application of MicroRNAs in Vascular Aging

Vascular aging, a specific type of organic aging, is related to age-dependent changes in the vasculature, including atherosclerotic plaques, arterial stiffness, fibrosis, and increased intimal thickening. Vascular aging could influence the threshold, process, and severity of various cardiovascular diseases, thus making it one of the most important risk factors in the high mortality of cardiovascular diseases. As endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) are the main cell biological basis of these pathology changes of the vasculature, the structure and function of ECs and VSMCs play a key role in vascular aging. MicroRNAs (miRNAs), small noncoding RNAs, have been shown to regulate the expression of multiple messenger RNAs (mRNAs) posttranscriptionally, contributing to many crucial aspects of cell biology. Recently, miRNAs with functions associated with aging or aging-related diseases have been studied. In this review, we will summarize the reported role of miRNAs in the process of vascular aging with special emphasis on EC and VSMC functions. In addition, the potential application of miRNAs to clinical practice for the diagnosis and treatment of cardiovascular diseases will also be discussed.

Multi-omics analysis reveals regulators of the response to PDGF-BB treatment in pulmonary artery smooth muscle cells

Background

Pulmonary arterial hypertension (PAH) is a lethal disease with pronounced narrowing of pulmonary vessels due to abnormal cell proliferation. The platelet-derived growth factor BB (PDGF-BB) is well known as a potent mitogen for smooth muscle cell proliferation. To better understand how this growth factor regulates pulmonary arterial smooth muscle cells (PASMCs) proliferation, we sought to characterize the response to PDGF-BB stimulation at system-wide levels, including the transcriptome and proteome.

Results

In this study, we identified 1611 mRNAs (transcriptome), 207 proteins (proteome) differentially expressed in response to PDGF-BB stimulation in PASMCs based on RNA-sequencing and isobaric tags for relative and absolute quantification (iTRAQ) assay. Transcription factor (TF)-target network analysis revealed that PDGF-BB regulated gene expression potentially via TFs including HIF1A, JUN, EST1, ETS1, SMAD1, FOS, SP1, STAT1, LEF1 and CEBPB. Among them, SMAD1-involved BMPR2/SMADs axis plays a significant role in PAH development. Interestingly, we observed that the expression of BMPR2 was decreased in both mRNA and protein level in response to PDGF-BB. Further study revealed that BMPR2 is the direct target of miR-376b that is up-regulated upon PDGF-BB treatment. Finally, EdU incorporation assay showed that miR-376b promoted proliferation of PASMCs.

Conclusion

This integrated analysis of PDGF-BB-regulated transcriptome and proteome was performed for the first time in normal PASMCs, which revealed a crosstalk between PDGF signaling and BMPR2/SMADs axis. Further study demonstrated that PDGF-BB-induced miR-376b upregulation mediated the downregulation of BMPR2, which led to expression change of its downstream targets and promoted proliferation of PASMCs.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3122-3) contains supplementary material, which is available to authorized users.

Ski diminishes TGF-β1-induced myofibroblast phenotype via up-regulating Meox2 expression

OBJECTIVE

The aim of the present work was to investigate the mechanism of transforming growth factor (TGF)-β1 and Sloan-Kettering Institute (Ski) in the pathogenesis of hypertrophic scars (HS).

BACKGROUND

Wound healing is an inherent process, but the aberrant wound healing of skin injury may lead to HS. There has been growing evidence suggesting a role for TGF-β1 and Ski in the pathogenesis of fibrosis.

MATERIAL AND METHODS

The MTT assay was used to detect the cell proliferation induced by TGF-β1. The Ski gene was transduced into cells with an adenovirus, and then the function of Ski in cell proliferation and differentiation was observed. Ski mRNA levels were measured by RT-PCR. Western blotting was used to detect the protein expression of α-SMA, E-cadherin, Meox1, Meox2, Zeb1 and Zeb2.

RESULTS

TGF-β1 can promote human skin fibroblast (HSF) cell proliferation in a time-dependent manner, but the promoting effect could be suppressed by Ski. TGF-β1 also induces the formation of the myofibroblast phenotype and the effect of TGF-β1 could be diminished by Ski. Also, Ski modulates the cardiac myofibroblast phenotype and function through suppression of Zeb2 by up-regulating the expression of Meox2.

CONCLUSIONS

Ski diminishes the myofibroblast phenotype induced by TGF-β1 through the suppression of Zeb2 by up-regulating the expression of Meox2.

c-Ski inhibits autophagy of vascular smooth muscle cells induced by oxLDL and PDGF

Autophagy is increasingly being recognized as a critical determinant of vascular smooth muscle cell (VSMC) biology. Previously, we have demonstrated that c-Ski inhibits VSMC proliferation stimulated by transforming growth factor β (TGF-β), but it is not clear whether c-Ski has the similar protective role against other vascular injury factors and whether regulation of autophagy is involved in its protective effects on VSMC. Accordingly, in this study, rat aortic A10 VSMCs were treated with 40 µg/ml oxidized low-density lipoprotein (oxLDL) or 20 ng/ml platelet-derived growth factor (PDGF), both of which were autophagy inducers and closely related to the abnormal proliferation of VSMCs. Overexpression of c-Ski in A10 cells significantly suppressed the oxLDL- and PDGF- induced autophagy. This action of c-Ski resulted in inhibiting the cell proliferation, the decrease of contractile phenotype marker α-SMA expression while the increase of synthetic phenotype marker osteopontin expression stimulated by oxLDL or PDGF. Inversely, knockdown of c-Ski by RNAi enhanced the stimulatory effects of oxLDL or PDGF on A10 cell growth and phenotype transition. And further investigation found that inhibition of AKT phosphorylation to downregulate proliferating cell nuclear antigen (PCNA) expression, was involved in the regulation of autophagy and associated functions by c-Ski in the oxLDL- and PDGF-stimulated VSMCs. Collectively, c-Ski may play an important role in inhibiting autophagy to protect VSMCs against some harsh stress including oxLDL and PDGF.

Alterations of the lung methylome in allergic airway hyper-responsiveness

Asthma is a chronic airway disorder characterized by recurrent attacks of breathlessness and wheezing, affecting 300 million people around the world (available at: www.who.int). To date, genetic factors associated with asthma susceptibility have been unable to explain the full etiology of asthma. Recent studies have demonstrated that the epigenetic disruption of gene expression plays an equally important role in the development of asthma through interaction with our environment. We sensitized 6-week-old C57BL/6J mice with house-dust-mite (HDM) extracts intraperitoneally followed by 5 weeks of exposure to HDM challenges (three times a week) intratracheally. HDM-exposed mice showed an increase in airway hyper-responsiveness (AHR) and inflammation together with structural remodeling of the airways. We applied methylated DNA immunoprecipitation-next generation sequencing (MeDIP-seq) for profiling of DNA methylation changes in the lungs in response to HDM. We observed about 20 million reads by a single-run of massive parallel sequencing. We performed bioinformatics and pathway analysis on the raw sequencing data to identify differentially methylated candidate genes in HDM-exposed mice. Specifically, we have revealed that the transforming growth factor beta signaling pathway is epigenetically modulated by chronic exposure to HDM. Here, we demonstrated that a specific allergen may play a role in AHR through an epigenetic mechanism by disrupting the expression of genes in lungs that might be involved in airway inflammation and remodeling. Our findings provide new insights into the potential mechanisms by which environmental allergens induce allergic asthma and such insights may assist in the development of novel preventive and therapeutic options for this debilitative disease.

Mechanisms of action of acetaldehyde in the up-regulation of the human α2(I) collagen gene in hepatic stellate cells: key roles of Ski, SMAD3, SMAD4, and SMAD7

Alcohol-induced liver fibrosis and eventually cirrhosis is a leading cause of death. Acetaldehyde, the first metabolite of ethanol, up-regulates expression of the human α2(I) collagen gene (COL1A2). Early acetaldehyde-mediated effects involve phosphorylation and nuclear translocation of SMAD3/4-containing complexes that bind to COL1A2 promoter to induce fibrogenesis. We used human and mouse hepatic stellate cells to elucidate the mechanisms whereby acetaldehyde up-regulates COL1A2 by modulating the role of Ski and the expression of SMADs 3, 4, and 7. Acetaldehyde induced up-regulation of COL1A2 by 3.5-fold, with concomitant increases in the mRNA (threefold) and protein (4.2- and 3.5-fold) levels of SMAD3 and SMAD4, respectively. It also caused a 60% decrease in SMAD7 expression. Ski, a member of the Ski/Sno oncogene family, is colocalized in the nucleus with SMAD4. Acetaldehyde induces translocation of Ski and SMAD4 to the cytoplasm, where Ski undergoes proteasomal degradation, as confirmed by the ability of the proteasomal inhibitor lactacystin to blunt up-regulation of acetaldehyde-dependent COL1A2, but not of the nonspecific fibronectin gene (FN1). We conclude that acetaldehyde up-regulates COL1A2 by enhancing expression of the transactivators SMAD3 and SMAD4 while inhibiting the repressor SMAD7, along with promoting Ski translocation from the nucleus to cytoplasm. We speculate that drugs that prevent proteasomal degradation of repressors targeting COL1A2 may have antifibrogenic properties.