Hyperplasia suppressor gene associates with smooth muscle alpha-actin and is involved in the redifferentiation of vascular smooth muscle cells

Experimental conditions and protein markers for redifferentiation of human coronary artery smooth muscle cells

A phenotype switch from contractile type to proliferative type of arterial smooth muscle cells is known as dedifferentiation, but to the best of our knowledge, little is known about redifferentiation of coronary artery smooth muscle cells. The purpose of the present study was to determine in vitro culture conditions for inducing redifferentiation of coronary artery smooth muscle cells. In addition, the present study aimed to determine protein markers for detection of redifferentiated arterial smooth muscle cells. Human coronary artery smooth muscle cells (HCASMCs) were cultured in the presence or absence of growth factors, including epidermal growth factor, fibroblast growth factor-B and insulin. Protein expression and migration activity of HCASMCs were evaluated using western blotting and migration assay, respectively. In HCASMCs 5 days after 100% confluency, expression levels of α-smooth muscle actin (α-SMA), calponin, caldesmon and SM22α were significantly increased, while expression levels of proliferation cell nuclear antigen (PCNA) and S100A4 and migration activity were significantly decreased, compared with the corresponding levels just after reaching 100% confluency, indicating that redifferentiation occurred. Redifferentiation was also induced in a low-density culture of HCASMCs in the medium without growth factors. When the culture medium for confluent cells was replaced daily with fresh medium, the expression levels of α-SMA, caldesmon, SM22α, PCNA and S100A4 and migration activity were not significantly different but the calponin expression was significantly increased compared with the levels in dedifferentiated cells just after reaching 100% confluency. Thus, redifferentiation was induced in HCASMCs by deprivation of growth factors from culture medium. The results suggested that α-SMA, caldesmon and SM22α, but not calponin, are markers of redifferentiation of HCASMCs.

Overexpression of the hyperplasia suppressor gene inactivates airway fibroblasts obtained from a rat model of chronic obstructive pulmonary disease by inhibiting the Wnt signaling pathway

The present study aimed to investigate the effects of hyperplasia suppressor gene (HSG) overexpression on the activation of airway fibroblasts in a rat model of chronic obstructive pulmonary disease (COPD) and assess the underlying molecular mechanisms. The rat model of COPD was established by injection of papain and confirmed by hematoxylin and eosin staining. Airway fibroblasts were identified using immunofluorescence, and HSG expression was facilitated by an HSG vector. Cell viability, apoptosis and the levels of matrix metallopeptidase-9 (MMP-9), platelet-derived growth factor (PDGF), and transforming growth factor-β1 (TGF-β1) were measured via Cell Counting Kit-8, flow cytometry and ELISA analyses, respectively, and potential mechanisms were detected by reverse transcription-quantitative polymerase chain reaction and western blotting. Airway fibroblasts from COPD rats were isolated and identified based on vimentin expression. Compared with the control group, HSG overexpression reduced cell viability, promoted apoptosis, and reduced the protein levels of TGF-β1, MMP-9 and PDGF. Additionally, HSG overexpression reduced β-catenin and Ras homology family member A (RhoA) expression at both the mRNA and protein levels. Conversely, Wnt signaling pathway agonists lithium chloride (LiCl) and 4-ethyl-5,6-dihydro-5-methyl- (1,3)dioxolo(4,5-j)phenanthridine (HLY78), significantly reduced the effects of HSG overexpression (P<0.05 vs. HSG). Cell viability in the HSG + LiCl and HSG + HLY78 groups was increased, whereas apoptosis was reduced compared with HSG treatment alone. The protein levels of TGF-β1, MMP-9 and PDGF were also decreased in the HSG + LiCl and HSG + HLY78 groups compared with the HSG group (P<0.05). Furthermore, the expression of β-catenin and RhoA was higher in the HSG + LiCl and HSG + HLY78 groups compared with the HSG group (P<0.05). Collectively, the results indicated that HSG overexpression inactivated airway fibroblasts from COPD by inhibiting the Wnt signaling pathway.

Flavonoids from Inula britannica reduces oxidative stress through inhibiting expression and phosphorylation of p47(phox) in VSMCs

CONTEXT

Inula britanica Linn. (Compositae) is a traditional Chinese medicinal herb that has been used to treat bronchitis and inflammation. The total flavonoid extracts (TFEs) isolated from its flowers can inhibit neointimal formation induced by balloon injury in vivo.

OBJECTIVE

To investigate the mechanism by which TFE suppresses oxidative stress generation and the subsequent inflammation response in vitro.

MATERIALS AND METHODS

The cultured vascular smooth muscle cells (VSMCs) form rats were exposed to oxidative stress following pretreatment with or without TFE at different concentration. Then, fluorescence staining was used to detect superoxide anion (O₂(˙-)) production, and the lever of maleic dialdehyde (MDA) and superoxide dismutase (SOD) was measured at the same time. Furthermore, tumor necrosis factor-α (TNF-α) was measured by enzyme linked immunosorbent assay (ELISA), reverse transcription-PCR and western blot were performed to detect the expression activity of p47(phox) gene, and immunoprecipitation was used to test the level of p47(phox) phosphorylation.

RESULTS

TFE inhibited the production of O₂(˙-) induced by H₂O₂ in VSMCs, with decrease in secretion of TNF-α; elevated the activity of SOD in the medium, similar to the effect of quercetin; reduced the level of MDA in culture medium of VSMCs. The pretreatment with TFE resulted in decrease the level of p47(phox) mRNA and protein, and even p47(phox) phosphorylation in VSMCs, compared with H₂O₂ control.

DISCUSSION AND CONCLUSION

These findings demonstrate that TFE is capable of attenuating the oxidative stress generation and the subsequent inflammation response via preventing the overexpression and activation of p47(phox) and the increased TNF-α secretion in VSMCs in vitro.

Vascular smooth-muscle-cell activation: proteomics point of view

Vascular smooth-muscle cells (VSMCs) are the main component of the artery medial layer. Thanks to their great plasticity, when stimulated by external inputs, VSMCs react by changing morphology and functions and activating new signaling pathways while switching others off. In this way, they are able to increase the cell proliferation, migration, and synthetic capacity significantly in response to vascular injury assuming a more dedifferentiated state. In different states of differentiation, VSMCs are characterized by various repertories of activated pathways and differentially expressed proteins. In this context, great interest is addressed to proteomics technology, in particular to differential proteomics. In recent years, many authors have investigated proteomics in order to identify the molecular factors putatively involved in VSMC phenotypic modulation, focusing on metabolic networks linking the differentially expressed proteins. Some of the identified proteins may be markers of pathology and become useful tools of diagnosis. These proteins could also represent appropriately validated targets and be useful either for prevention, if related to early events of atherosclerosis, or for treatment, if specific of the acute, mid, and late phases of the pathology. RNA-dependent gene silencing, obtained against the putative targets with high selective and specific molecular tools, might be able to reverse a pathological drift and be suitable candidates for innovative therapeutic approaches.

Krüppel-like factor 4 interacts with p300 to activate mitofusin 2 gene expression induced by all-trans retinoic acid in VSMCs

AIM

To elucidate how krüppel-like factor 4 (KLF4) activates mitofusin 2 (mfn-2) expression in all-trans retinoic acid (ATRA)-induced vascular smooth muscle cell (VSMC) differentiation.

METHODS

The mfn-2 promoter-reporter constructs and the KLF4 acetylation-deficient or phosphorylation-deficient mutants were constructed. Adenoviral vector of KLF4-mediated overexpression and Western blot analysis were used to determine the effect of KLF4 on mfn-2 expression. The luciferase assay and chromatin immunoprecipitation were used to detect the transactivation of KLF4 on mfn-2 gene expression. Co-immunoprecipitation and GST pull-down assays were used to determine the modification of KLF4 and interaction of KLF4 with p300 in VSMCs.

RESULTS

KLF4 mediated ATRA-induced mfn-2 expression in VSMCs. KLF4 bound directly to the mfn-2 promoter and activated its transcription. ATRA increased the interaction of KLF4 with p300 by inducing KLF4 phosphorylation via activation of JNK and p38 MAPK signaling. KLF4 acetylation by p300 increased its activity to transactivate the mfn-2 promoter.

CONCLUSION

ATRA induces KLF4 acetylation by p300 and increases the ability of KLF4 to transactivate the mfn-2 promoter in VSMCs.

hhLIM is a novel F-actin binding protein involved in actin cytoskeleton remodeling

Human heart LIM protein (hhLIM) is a newly cloned protein. In vitro analyses showed that green fluorescent protein (GFP)-tagged hhLIM protein accumulated in the cytoplasm of C2C12 cells and colocalized with F-actin, indicating that hhLIM is an actin-binding protein in C2C12 cells. Overexpression of hhLIM-GFP in C2C12 cells significantly stabilized actin filaments and delayed depolymerization of the actin cytoskeleton induced by cytochalasin B treatment. Expression of hhLIM-GFP in C2C12 cells also induced significant changes in the organization of the actin cytoskeleton, specifically, fewer and thicker actin bundles than in control cells, suggesting that hhLIM functions as an actin-bundling protein. This hypothesis was confirmed using low-speed co-sedimentation assays and direct observation of F-actin bundles that formed in vitro in the presence of hhLIM. hhLIM has two LIM domains. To identify the essential regions and sites for association, a series of truncated mutants was constructed which showed that LIM domain 2 has the same activity as full-length hhLIM. To further characterize the binding sites, the LIM domain was functionally destructed by replacing cysteine with serine in domain 2, and results showed that the second LIM domain plays a central role in bundling of F-actin. Taken together, these data identify hhLIM as an actin-binding protein that increases actin cytoskeleton stability by promoting bundling of actin filaments.

Human heart LIM protein activates atrial-natriuretic-factor gene expression by interacting with the cardiac-restricted transcription factor Nkx2.5

hhLIM [human heart LIM (Lin-11/IsI-1/Mec-3) protein] is a muscle-specific LIM-only protein that consists of two LIM motifs. hhLIM functions as a positive regulator for cardiac hypertrophy. Here we report that hhLIM serves as a cofactor regulating the expression of the ANF (atrial natriuretic factor) gene in H9c2 rat cardiomyoblast cells. We found that hhLIM promoted the expression of the ANF gene in H9c2 cells, but not in A293 human embryonic kidney cells. Furthermore, we showed that hhLIM interacted with Nkx2.5 (a cardiac-restricted transcription factor) in vivo and in vitro using its N-terminal LIM domain and enhanced the binding ability of Nkx2.5 to the NKE (Nkx2.5-binding element) boxes in the ANF promoter. These results suggest that hhLIM promotes the specific expression of the ANF gene by co-operating with Nkx2.5.