The four-and-a-half LIM domain protein 2 regulates vascular smooth muscle phenotype and vascular tone

FHL2 in arterial medial calcification in chronic kidney disease

BACKGROUND

Arterial medial calcification (AMC) is a common complication in individuals with chronic kidney disease (CKD), which can lead to cardiovascular morbidity and mortality. The progression of AMC is controlled by a key transcription factor called runt-related transcription factor 2 (RUNX2), which induces vascular smooth muscle cells (VSMCs) transdifferentiation into an osteogenic phenotype. However, RUNX2 has not been targeted for therapy due to its essential role in bone development. The objective of our study was to discover a RUNX2 coactivator that is highly expressed in arterial VSMCs as a potential therapy for AMC.

METHODS

We employed transcriptomic analysis of human data and an animal reporter system to pinpoint four and a half LIM domains 2 (FHL2) as a potential target. Subsequently, we investigated the mRNA and protein expression patterns of FHL2 in the aortas of both human and animal subjects with CKD. To examine the role of FHL2 in the RUNX2 transcription machinery, we conducted coimmunoprecipitation and chromatin immunoprecipitation experiments. Next, we manipulated FHL2 expression in cultured VSMCs to examine its impact on high phosphate-induced transdifferentiation. Finally, we employed FHL2-null mice to confirm the role of FHL2 in the development of AMC in vivo.

RESULTS

Among all the potential RUNX2 cofactors, FHL2 displays selective expression within the cardiovascular system. In the context of CKD subjects, FHL2 undergoes upregulation and translocation from the cytosol to the nucleus of arterial VSMCs. Once in the nucleus, FHL2 interacts structurally and functionally with RUNX2, acting as a coactivator of RUNX2. Notably, the inhibition of FHL2 expression averts transdifferentiation of VSMCs into an osteogenic phenotype and mitigates aortic calcification in uremic animals, without causing any detrimental effects on the skeletal system.

CONCLUSION

These observations provide evidence that FHL2 is a promising target for treating arterial calcification in patients with CKD.

Unlocking the secrets of Cardiac development and function: the critical role of FHL2

FHL2 (Four-and-a-half LIM domain protein 2) is a crucial factor involved in cardiac morphogenesis, the process by which the heart develops its complex structure. It is expressed in various tissues during embryonic development, including the developing heart, and has been shown to play important roles in cell proliferation, differentiation, and migration. FHL2 interacts with multiple proteins to regulate cardiac development as a coactivator or a corepressor. It is involved in cardiac specification and determination of cell fate, cardiomyocyte growth, cardiac remodeling, myofibrillogenesis, and the regulation of HERG channels. Targeting FHL2 has therapeutic implications as it could improve cardiac function, control arrhythmias, alleviate heart failure, and maintain cardiac integrity in various pathological conditions. The identification of FHL2 as a signature gene in atrial fibrillation suggests its potential as a diagnostic marker and therapeutic target for this common arrhythmia.

Convergence of coronary artery disease genes onto endothelial cell programs

Linking variants from genome-wide association studies (GWAS) to underlying mechanisms of disease remains a challenge1-3. For some diseases, a successful strategy has been to look for cases in which multiple GWAS loci contain genes that act in the same biological pathway1-6. However, our knowledge of which genes act in which pathways is incomplete, particularly for cell-type-specific pathways or understudied genes. Here we introduce a method to connect GWAS variants to functions. This method links variants to genes using epigenomics data, links genes to pathways de novo using Perturb-seq and integrates these data to identify convergence of GWAS loci onto pathways. We apply this approach to study the role of endothelial cells in genetic risk for coronary artery disease (CAD), and discover 43 CAD GWAS signals that converge on the cerebral cavernous malformation (CCM) signalling pathway. Two regulators of this pathway, CCM2 and TLNRD1, are each linked to a CAD risk variant, regulate other CAD risk genes and affect atheroprotective processes in endothelial cells. These results suggest a model whereby CAD risk is driven in part by the convergence of causal genes onto a particular transcriptional pathway in endothelial cells. They highlight shared genes between common and rare vascular diseases (CAD and CCM), and identify TLNRD1 as a new, previously uncharacterized member of the CCM signalling pathway. This approach will be widely useful for linking variants to functions for other common polygenic diseases.

How (Epi)Genetic Regulation of the LIM-Domain Protein FHL2 Impacts Multifactorial Disease

Susceptibility to complex pathological conditions such as obesity, type 2 diabetes and cardiovascular disease is highly variable among individuals and arises from specific changes in gene expression in combination with external factors. The regulation of gene expression is determined by genetic variation (SNPs) and epigenetic marks that are influenced by environmental factors. Aging is a major risk factor for many multifactorial diseases and is increasingly associated with changes in DNA methylation, leading to differences in gene expression. Four and a half LIM domains 2 (FHL2) is a key regulator of intracellular signal transduction pathways and the FHL2 gene is consistently found as one of the top hyper-methylated genes upon aging. Remarkably, FHL2 expression increases with methylation. This was demonstrated in relevant metabolic tissues: white adipose tissue, pancreatic β-cells, and skeletal muscle. In this review, we provide an overview of the current knowledge on regulation of FHL2 by genetic variation and epigenetic DNA modification, and the potential consequences for age-related complex multifactorial diseases.

Early Programming of Adult Systemic Essential Hypertension

Cardiovascular diseases are being included in the study of developmental origins of health and disease (DOHaD) and essential systemic hypertension has also been added to this field. Epigenetic modifications are one of the main mechanisms leading to early programming of disease. Different environmental factors occurring during critical windows in the early stages of life may leave epigenetic cues, which may be involved in the programming of hypertension when individuals reach adulthood. Such environmental factors include pre-term birth, low weight at birth, altered programming of different organs such as the blood vessels and the kidney, and living in disadvantageous conditions in the programming of hypertension. Mechanisms behind these factors that impact on the programming include undernutrition, oxidative stress, inflammation, emotional stress, and changes in the microbiota. These factors and their underlying causes acting at the vascular level will be discussed in this paper. We also explore the establishment of epigenetic cues that may lead to hypertension at the vascular level such as DNA methylation, histone modifications (methylation and acetylation), and the role of microRNAs in the endothelial cells and blood vessel smooth muscle which participate in hypertension. Since epigenetic changes are reversible, the knowledge of this type of markers could be useful in the field of prevention, diagnosis or epigenetic drugs as a therapeutic approach to hypertension.

Deletion of the FHL2 gene attenuates intima-media thickening in a partially ligated carotid artery ligated mouse model

The four and a half LIM domain protein 2 (FHL2) is a member of the four and a half LIM domain (FHL) gene family, and it is associated with cholesterol‐enriched diet‐promoted atherosclerosis. However, the effect of FHL2 protein on vascular remodelling in response to hemodynamic alterations remains unclear. Here, we investigated the role of FHL2 in a model of restricted blood flow‐induced atherosclerosis. To promote neointimal hyperplasia in vivo, we subjected FHL2^+/+ and FHL2^−/− mice to partial ligation of the left carotid artery (LCA). The expression of p‐ERK and p‐AKT was decreased in FHL2^−/− mice. FHL2 bound to AKT regulated AKT phosphorylation and led to Rac1‐GTP inactivation. FHL2 silencing in human aortic smooth muscle cells down‐regulated the PDGF‐induced phosphorylation of ERK and AKT. Furthermore, FHL2 silencing reduced cytoskeleton conformational changes and caused cell cycle arrest. We concluded that FHL2 is essential for the regulation of arterial smooth muscle cell function. FHL2 modulates proliferation and migration via mitogen‐activated protein kinase (MAPK) and PI3K‐AKT signalling, leading to arterial wall thickening and thus neointimal hyperplasia.

5-Lipoxagenase deficiency attenuates L-NAME-induced hypertension and vascular remodeling

BACKGROUND

Abnormalities of the L-arginine-nitric oxide pathway induce hypertension. 5-Lipoxygenase (5-LO) is the key enzyme involved in synthesis of leukotrienes (LTs). However, whether nitricoxide synthase dysfunction induces hypertensive vascular remodeling by regulating 5-LO activity and its downstream inflammatory metabolites remains unknown.

METHODS AND RESULTS

Six-week L-NAME treatment significantly induced hypertension and vascular remodeling in both wild-type (WT) and 5-LO-knockout (5-LO-KO) mice, and blood pressure in caudal and carotid arteries was lower in 5-LO-KO than WT mice with L-NAME exposure. On histology, L-NAME induced less media thickness, media-to-lumen ratio, and collagen deposition and fewer Ki-67-positive vascular smooth muscle cells (VSMCs) but more elastin expression in thoracic and mesenteric aortas of 5-LO-KO than L-NAME-treated WT mice. L-NAME significantly increased LT content, including LTB4 and cysteinyl LT (CysLTs), in plasma and neutrophil culture supernatants from WT mice. On immunohistochemistry, L-NAME promoted the colocalization of 5-LO and 5-LO-activating protein on the nuclear envelope of cultured neutrophils, which was accompanied by elevated LT content in culture supernatants. In addition, LTs significantly promoted BrdU incorporation, migration and phenotypic modulation in VSMCs.

CONCLUSION

L-NAME may activate the 5-LO/LT pathway in immune cells, such as neutrophils, and promote the products of 5-LO metabolites, including LTB4 and CysLTs, which aggravate vascular remodeling in hypertension. 5-LO deficiency may protect against hypertension and vascular remodeling by reducing levels of 5-LO downstream inflammatory metabolites.

Matrine blocks AGEs- induced HCSMCs phenotypic conversion via suppressing Dll4-Notch pathway

Vascular smooth muscle cells (VSMCs) contractile- synthetic phenotypic conversion takes responsibility in the atherosclerotic plaque formation by abnormal synthesis, secretion and deposition of extracellular matrix (ECM). Matrine exerts therapeutic effects on both cardiovascular diseases and organ fibrosis. In this study, we investigated matrine's inhibitory effect and mechanisms on AGEs- induced VSMC contractile- synthetic phenotypic conversion. Cultured human coronary smooth muscle cells (HCSMCs) were exposed to AGEs. Matrine at serially diluted concentrations were used to treat the cells. HCSMCs phenotype was identified by immunofluorescent staining of contractile phenotypic markers including mooth muscle myosin heavy chain (MYH11) and smooth muscle α-actin (ACTA2). Sircol collagen assay was used to assess the collagen secretion level. Notch signaling activation was determined by luciferase assay. Western blotting was used to evaluate expression levels of collagen I, collagen VIII, Delta-like (Dll)1, Dll3, Dll4, Jagged1, Jagged2, Notch intracellular domain (NICD)1 and Hes family basic helix-loop-helix (bHLH) transcription factor1 (HES1). Matrine pre-treatment recovered the AGEs- induced contractile- synthetic phenotypic conversion by increasing MYH11 and ACTA2 in HCSMCs. Matrine reduced AGEs- mediated activation of Notch signaling, down-regulated expression levels of NICD1, HES1, collagen I and collagen VIII and collagen secretion contents in HCSMCs. Matrine inhibited expression level of Dll4 without affecting other Notch ligands including Dll1, Dll3, Jagged1 and Jagged2 in HCSMCs exposed to AGEs. These results suggested that AGEs exposure facilitated the contractile- synthetic phenotypic conversion of HCSMCs. Matrine blocked this phenotypic conversion by suppressing Dll4- Notch signaling pathway activation.

Protein-protein interactions of the LIM-only protein FHL2 and functional implication of the interactions relevant in cardiovascular disease

FHL2 belongs to the LIM-domain only proteins and contains four and a half LIM domains, each of which are composed of two zinc finger structures. FHL2 exhibits specific interaction with proteins exhibiting diverse functions, including transmembrane receptors, transcription factors and transcription co-regulators, enzymes, and structural proteins. The function of these proteins is regulated by FHL2, which modulates intracellular signal transduction pathways involved in a plethora of cellular tasks. The present review summarizes the current knowledge on the protein interactome of FHL2 and provides an overview of the functional implication of these interactions in apoptosis, migration, and regulation of nuclear receptor function. FHL2 was originally identified in the heart and there is extensive literature available on the role of FHL2 in the cardiovascular system, which is also summarized in this review.

Absence of Four-and-a-Half LIM Domain Protein 2 Decreases Atherosclerosis in ApoE −/− Mice

Objective—

Four-and-a-half LIM domain protein-2 (FHL2) is expressed in endothelial cells, vascular smooth muscle cells, and leukocytes. It regulates cell survival, migration, and inflammatory response, but its role in atherogenesis is unknown.

Approach and Results—

To investigate the role of FHL2 in atherosclerosis, FHL2-deficient mice were crossed with ApoE-deficient mice, to generate ApoE/FHL2−/− mice. After high-fat diet, ApoE/FHL2−/− mice had significantly smaller atherosclerotic plaques than ApoE−/− mice in the aortic sinus, the brachiocephalic artery, and the aorta. This was associated with enhanced collagen and smooth muscle cell contents and a 2-fold reduction in macrophage content within the plaques of ApoE/FHL-2−/− versus ApoE−/− mice. This could be explained, in part, by the reduction in aortic ICAM-1 (intracellular adhesion molecule) mRNA and VCAM-1 (vascular cell adhesion molecule) protein expression in the plaque. Aortic gene expression of the chemokines CX3CL1 and CCL5 was increased in ApoE/FHL2−/− versus ApoE−/− mice. Peritoneal thioglycollate injection elicited equivalent numbers of monocytes and macrophages in both groups, but a significantly lower number of proinflammatory Ly6C high monocytes were recruited in ApoE/FHL2−/− versus ApoE−/− mice. Furthermore, mRNA levels of CX3CR1 were 2-fold higher in monocytes from ApoE/FHL2−/− versus ApoE−/− mice. Finally, we investigated the potential importance of myeloid cell FHL2 deficiency in atherosclerosis. After being irradiated, ApoE−/− or ApoE/FHL2−/− mice were transplanted with ApoE−/− or ApoE/FHL2−/− bone marrow. After high-fat diet, both chimeric groups developed smaller plaques than ApoE−/− transplanted with ApoE−/− bone marrow.

Conclusions—

These results suggest that FHL2 in both myeloid and vascular cells may play an important role in atherosclerosis by promoting proinflammatory chemokine production, adhesion molecule expression, and proinflammatory monocyte recruitment.

Ubiquitinated proteins enriched from tumor cells by a ubiquitin binding protein Vx3(A7) as a potent cancer vaccine

Background

Our previous studies have demonstrated that autophagosome-enriched vaccine (named DRibbles: DRiPs-containing blebs) induce a potent anti-tumor efficacy in different murine tumor models, in which DRibble-containing ubiquitinated proteins are efficient tumor-specific antigen source for the cross-presentation after being loaded onto dendritic cells. In this study, we sought to detect whether ubiquitinated proteins enriched from tumor cells could be used directly as a novel cancer vaccine.

Methods

The ubiquitin binding protein Vx3(A7) was used to isolate ubiquitinated proteins from EL4 and B16-F10 tumor cells after blocking their proteasomal degradation pathway. C57BL/6 mice were vaccinated with different doses of Ub-enriched proteins via inguinal lymph nodes or subcutaneous injection and with DRibbles, Ub-depleted proteins and whole cell lysate as comparison groups, respectively. The lymphocytes from the vaccinated mice were re-stimulated with inactivated tumor cells and the levels of IFN-γ in the supernatant were detected by ELISA. Anti-tumor efficacy of Ub-enriched proteins vaccine was evaluated by monitoring tumor growth in established tumor mice models. Graphpad Prism 5.0 was used for all statistical analysis.

Results

We found that after stimulation with inactivated tumor cells, the lymphocytes from the Ub-enriched proteins-vaccinated mice secreted high level of IFN-γ in dose dependent manner, in which the priming vaccination via inguinal lymph nodes injection induced higher IFN-γ level than that via subcutaneous injection. Moreover, the level of secreted IFN-γ in the Ub-enriched proteins group was markedly higher than that in the whole cell lysate and Ub-depleted proteins. Interestingly, the lymphocytes from mice vaccinated with Ub-enriched proteins, but not Ub-depleted proteins and whole cell lysates, isolated from EL4 or B16-F10 tumor cells also produced an obvious level of IFN-γ when stimulated alternately with inactivated B16-F10 or EL4 tumor cells. Furthermore, Ub-enriched proteins vaccine showed a significant inhibitory effect on in vivo growth of homologous tumor, as well as allogeneic tumor, compared with Ub-depleted proteins and tumor cell lysate. Tumor growth was regressed after three times of vaccination with Ub-enriched proteins in contrast to other groups.

Conclusion

These results indicated that Ub-enriched proteins isolated from tumor cells may have a potential as a potent vaccine for immunotherapy against cancer.

The activity of satellite cells and myonuclei following 8 weeks of strength training in young men with suppressed testosterone levels

AIM

To investigate how suppression of endogenous testosterone during an 8-week strength training period influences the activity of satellite cells and myonuclei.

METHODS

Twenty-two moderately trained young men participated in this randomized, placebo-controlled, and double-blinded intervention study. The participants were randomized to treatment with a GnRH analogue, goserelin (n = 12), which suppresses testosterone or placebo (n = 10) for 12 weeks. The strength training period of 8 weeks started after 4 weeks of treatment and included exercises for all major muscles. Biopsies were obtained from the mid-portion of the vastus lateralis muscle.

RESULTS

Testosterone resting level in goserelin was 10-20 times lower compared with placebo, and the training-induced increase in the level of testosterone was abolished in goserelin. Training increased satellite cells number in type II fibres by 20% in placebo and by 52% in goserelin (P < 0.01), whereas the myonuclear number significantly increased by 12% in type II fibres in placebo and remained unchanged in goserelin (P < 0.05). No changes in satellite cells and myonuclei were seen in type I fibres in either group. Data from the microarray analysis indicated that low testosterone affects the bone morphogenetic proteins signalling, which might regulate proliferation vs. differentiation of satellite cells.

CONCLUSION

Eight weeks of strength training enhances the myonuclear number in type II fibres, and this is largely blocked by the suppression of testosterone. The data indicate that low testosterone levels could reduce the differentiation of satellite cells to myonuclei via the bone morphogenetic proteins signalling pathway, resulting in reduced increases in lean leg mass.

LIM-only protein FHL2 is a positive regulator of liver X receptors in smooth muscle cells involved in lipid homeostasis

The LIM-only protein FHL2 is expressed in smooth muscle cells (SMCs) and inhibits SMC-rich-lesion formation. To further elucidate the role of FHL2 in SMCs, we compared the transcriptomes of SMCs derived from wild-type (WT) and FHL2 knockout (KO) mice. This revealed that in addition to the previously recognized involvement of FHL2 in SMC proliferation, the cholesterol synthesis and liver X receptor (LXR) pathways are altered in the absence of FHL2. Using coimmunoprecipitation experiments, we found that FHL2 interacts with the two LXR isoforms, LXRα and LXRβ. Furthermore, FHL2 strongly enhances transcriptional activity of LXR element (LXRE)-containing reporter constructs. Chromatin immunoprecipitation (ChIP) experiments on the ABCG1 promoter revealed that FHL2 enhances the association of LXRβ with DNA. In line with these observations, we observed reduced basal transcriptional LXR activity in FHL2-KO SMCs compared to WT SMCs. This was also reflected in reduced expression of LXR target genes in intact aorta and aortic SMCs of FHL2-KO mice. Functionally, the absence of FHL2 resulted in attenuated cholesterol efflux to both ApoA-1 and high-density lipoprotein (HDL), in agreement with reduced LXR signaling. Collectively, our findings demonstrate that FHL2 is a transcriptional coactivator of LXRs and points toward FHL2 being an important determinant of cholesterol metabolism in SMCs.

The LIM-only protein FHL2 reduces vascular lesion formation involving inhibition of proliferation and migration of smooth muscle cells

The LIM-only protein FHL2, also known as DRAL or SLIM3, has a function in fine-tuning multiple physiological processes. FHL2 is expressed in the vessel wall in smooth muscle cells (SMCs) and endothelial cells and conflicting data have been reported on the regulatory function of FHL2 in SMC phenotype transition. At present the function of FHL2 in SMCs in vascular injury is unknown. Therefore, we studied the role of FHL2 in SMC-rich lesion formation. In response to carotid artery ligation FHL2-deficient (FHL2-KO) mice showed accelerated lesion formation with enhanced Ki67 expression compared with wild-type (WT)-mice. Consistent with these findings, cultured SMCs from FHL2-KO mice showed increased proliferation through enhanced phosphorylation of extracellular-regulated kinase-1/2 (ERK1/2) and induction of CyclinD1 expression. Overexpression of FHL2 in SMCs inhibited CyclinD1 expression and CyclinD1-knockdown blocked the enhanced proliferation of FHL2-KO SMCs. We also observed increased CyclinD1 promoter activity in FHL2-KO SMCs, which was reduced upon ERK1/2 inhibition. Furthermore, FHL2-KO SMCs showed enhanced migration compared with WT SMCs. In conclusion, FHL2 deficiency in mice results in exacerbated SMC-rich lesion formation involving increased proliferation and migration of SMCs via enhanced activation of the ERK1/2-CyclinD1 signaling pathway.

Inhibition of four-and-a-half LIM domain protein-2 increases survival, migratory capacity, and paracrine function of human early outgrowth cells through activation of the sphingosine kinase-1 pathway: implications for endothelial regeneration

RATIONALE

Inhibition of four-and-a-half LIM domain protein-2 (FHL2) attenuates atherosclerotic lesion formation and increases endothelial cell migration. Early outgrowth cells (EOCs) contribute substantially to endothelial repair.

OBJECTIVE

We investigated the role of FHL2 in the regulation of EOCs.

METHODS AND RESULTS

Human EOCs were cultured from peripheral blood. FHL2 knockdown in EOCs by siRNA resulted in increased EOC numbers and reduced apoptosis, as indicated by decreased cleaved caspase-III and reduced Bax/Bcl-2 expression ratio. This was mediated through increased phosphorylation and membrane translocation of sphingosine kinase-1, increased sphingosine-1-phosphate levels, and Akt phosphorylation. FHL2 knockdown increased stromal cell-derived factor-1-induced EOC migration through upregulation of αv/β3, αv/β5, and β2 integrins, associated with increased cortactin expression. Reduced apoptosis, increased EOC migration, and cortactin upregulation by FHL2 siRNA were prevented by CAY10621, the sphingosine kinase-1 inhibitor, and the sphingosine-1-phosphate receptor-1/-3 antagonist VPC23019. These findings were confirmed using spleen-derived EOCs from FHL2(-/-) mice. Apoptosis was decreased and migration increased in endothelial cells exposed to the conditioned medium of FHL2(-/-) versus wild-type (WT) EOCs. These paracrine effects were abolished by VPC23019. Importantly, reendothelialization after focal carotid endothelial injury in WT mice was significantly increased after intravenous injection of FHL2(-/-) versus WT EOCs.

CONCLUSIONS

Our findings suggest that FHL2 negatively regulates EOC survival, migration, and paracrine function. FHL2 inhibition in EOCs reduces apoptosis and enhances survival and migratory capacity of both EOCs and surrounding endothelial cells by activation of the sphingosine kinase-1/sphingosine-1-phosphate pathway, resulting in improvement of endothelial regeneration.

Endoglin-mediated suppression of prostate cancer invasion is regulated by activin and bone morphogenetic protein type II receptors

Mortality from prostate cancer (PCa) is due to the formation of metastatic disease. Understanding how that process is regulated is therefore critical. We previously demonstrated that endoglin, a type III transforming growth factor β (TGFβ) superfamily receptor, suppresses human PCa cell invasion and metastasis. Endoglin-mediated suppression of invasion was also shown by us to be dependent upon the type I TGFβ receptor, activin receptor-like kinase 2 (ALK2), and the downstream effector, Smad1. In this study we demonstrate for the first time that two type II TGFβ receptors are required for endoglin-mediated suppression of invasion: activin A receptor type IIA (ActRIIA) and bone morphogenetic protein receptor type II (BMPRII). Downstream signaling through these receptors is predominantly mediated by Smad1. ActRIIA stimulates Smad1 activation in a kinase-dependent manner, and this is required for suppression of invasion. In contrast BMPRII regulates Smad1 in a biphasic manner, promoting Smad1 signaling through its kinase domain but suppressing it through its cytoplasmic tail. BMPRII’s Smad1-regulatory effects are dependent upon its expression level. Further, its ability to suppress invasion is independent of either kinase function or tail domain. We demonstrate that ActRIIA and BMPRII physically interact, and that each also interacts with endoglin. The current findings demonstrate that both BMPRII and ActRIIA are necessary for endoglin-mediated suppression of human PCa cell invasion, that they have differential effects on Smad1 signaling, that they make separate contributions to regulation of invasion, and that they functionally and physically interact.

A molecular mechanism for therapeutic effects of cGMP-elevating agents in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a progressive, usually fatal disease with abnormal vascular remodeling. Pulmonary artery smooth muscle cells (PASMCs) from PAH patients are hyperproliferative and apoptosis-resistant and demonstrate decreased signaling in response to bone morphogenetic proteins (BMPs). Cyclic GMP-elevating agents are beneficial in PAH, but their mechanism(s) of action are incompletely understood. Here we show that BMP signaling via Smad1/5/8 requires cGMP-dependent protein kinase isotype I (PKGI) to maintain PASMCs in a differentiated, low proliferative state. BMP cooperation with cGMP/PKGI was crucial for transcription of contractile genes and suppression of pro-proliferative and anti-apoptotic genes. Lungs from mice with low or absent PKGI (Prkg1(+/-) and Prkg1(-/-) mice) exhibited impaired BMP signaling, decreased contractile gene expression, and abnormal vascular remodeling. Conversely, cGMP stimulation of PKGI restored defective BMP signaling in rats with hypoxia-induced PAH, consistent with cGMP-elevating agents reversing vascular remodeling in this PAH model. Our results provide a mechanism for the therapeutic effects of cGMP-elevating agents in PAH and suggest that combining them with BMP mimetics may provide a novel, disease-modifying approach to PAH therapy.

Basic fibroblast growth factor gene transfection in repair of internal carotid artery aneurysm wall

Surgery or interventional therapy has some risks in the treatment of cerebral aneurysm. We established an internal carotid artery aneurysm model by dripping elastase in the crotch of the right internal and external carotid arteries of New Zealand rabbits. Following model induction, lentivirus carrying basic fibroblast growth factor was injected through the ear vein. We found that the longer the action time of the lentivirus, the smaller the aneurysm volume. Moreover, platelet-derived growth factor expression in the aneurysm increased, but smooth muscle 22 alpha and hypertension-related gene 1 mRNA expression decreased. At 1, 2, 3, and 4 weeks following model establishment, following 1 week of injection of lentivirus carrying basic fibroblast growth factor, the later the intervention time, the more severe the blood vessel damage, and the bigger the aneurysm volume, the lower the smooth muscle 22 alpha and hypertension-related gene 1 mRNA expression. Simultaneously, platelet-derived growth factor expression decreased. These data suggest that recombinant lentivirus carrying basic fibroblast growth factor can repair damaged cells in the aneurysmal wall and inhibit aneurysm dynamic growth, and that the effect is dependent on therapeutic duration.

Inhibition of microRNA-302 (miR-302) by bone morphogenetic protein 4 (BMP4) facilitates the BMP signaling pathway

The signaling pathway mediated by BMPs plays an essential role during development as well as the maintenance of homeostasis in adult. Aberrant activation or inactivation of BMP signaling can lead to developmental defects and various human disorders. To fine-tune its activity, BMP signaling is regulated both positively and negatively by extrinsic and intrinsic regulatory factors that modulate binding of ligand to the receptors, and the activity of receptors and their dedicated signal transducers, the Smad proteins. Upon BMP binding to the receptor complex, Smad proteins translocate to the nucleus and modulate gene expression transcriptionally by directly associating with the promoter region of target genes, or post-transcriptionally through modulation of microRNA (miRNA) synthesis. In this study, we demonstrate that BMP signaling down-regulates transcription of the miRNA-302∼367 gene cluster. We show that the type II BMP receptor (BMPRII) is a novel target of miR-302. Upon overexpression, miR-302 targets a partially complementary sequence localized in the 3'-untranslated region (UTR) of BMPRII transcripts and leads to destabilization of the transcripts and down-regulation of BMP signaling. We propose that the negative regulatory loop of BMP4-miR-302-BMPRII is a potential mechanism for the maintenance and fine-tuning of the BMP signaling pathway in various systems.

FHL2 protein is a novel co-repressor of nuclear receptor Nur77

The three members of the NR4A orphan nuclear receptor subfamily Nur77, Nurr1, and NOR-1, regulate a variety of biological functions including vascular disease and metabolism. In this study, we identified Four and a half LIM domains protein-2 (FHL2) as a novel interacting protein of NR4A nuclear receptors by yeast two-hybrid screen and co-immunoprecipitation studies. Each of the four LIM domains of FHL2 can bind Nur77, and both the amino-terminal domain and the DNA binding domain of Nur77 are involved in the interaction between FHL2 and Nur77. FHL2 represses Nur77 transcriptional activity in a dose-dependent manner, and short hairpin RNA-mediated knockdown of FHL2 results in increased Nur77 transcriptional activity. ChIP experiments on the enolase3 promoter revealed that FHL2 inhibits the association of Nur77 with DNA. FHL2 is highly expressed in human endothelial and smooth muscle cells, but not in monocytes or macrophages. To substantiate functional involvement of FHL2 in smooth muscle cell physiology, we demonstrated that FHL2 overexpression increases the growth of these cells, whereas FHL2 knockdown results in reduced DNA synthesis. Collectively, these studies suggest that association of FHL2 with Nur77 plays a pivotal role in vascular disease.

down-regulation of Kruppel-like factor-4 (KLF4) by microRNA-143/145 is critical for modulation of vascular smooth muscle cell phenotype by transforming growth factor-beta and bone morphogenetic protein 4

In the postnatal vasculature, fully differentiated and quiescent vascular smooth muscle cells (VSMCs) in a "contractile" phenotype are required for the normal regulation of vascular tone. The transforming growth factor-β (TGF-β) superfamily of growth factors (TGF-βs and bone morphogenetic proteins (BMPs)) are potent inducers of contractile phenotype and mediate (i) induction of contractile genes, and (ii) inhibition of VSMC growth and migration. Transcription of contractile genes is positively regulated by a regulatory DNA element called a CArG box. The CArG box is activated by the binding of serum response factor and its coactivators, myocardin (Myocd) or Myocd-related transcription factors (MRTFs). Krüppel-like factor-4 (KLF4) is known to inhibit activation of the CArG box. However, the potential role of KLF4 in the contractile activities of TGF-β or BMP has not been explored. Here, we demonstrate that TGF-β and BMP4 rapidly down-regulate KLF4 through induction of microRNA-143 (miR-143) and miR-145, which leads to a reduction of KLF4 transcripts and decreased KLF4 protein expression. Inhibition of miR-145 prevents down-regulation of KLF4 and activation of contractile genes by TGF-β or BMP4, suggesting that modulation of KLF4 is a prerequisite for induction of contractile genes by TGF-β and BMP4. Interestingly, both TGF-β and BMP4 activate transcription of the miR-143/145 gene cluster through the CArG box, however, TGF-β mediates this effect through induction of Myocd expression, whereas BMP4 utilizes nuclear translocation of MRTF-A. Thus, this study sheds light on both the similarities and the differences of TGF-β and BMP4 signaling in the regulation of KLF4 and contractile genes.

The amiloride derivative phenamil attenuates pulmonary vascular remodeling by activating NFAT and the bone morphogenetic protein signaling pathway

Pulmonary artery hypertension (PAH) is characterized by elevated pulmonary artery resistance and increased medial thickness due to deregulation of vascular remodeling. Inactivating mutations of the BMPRII gene, which encodes a receptor for bone morphogenetic proteins (BMPs), are identified in ∼60% of familial PAH (FPAH) and ∼30% of idiopathic PAH (IPAH) patients. It has been hypothesized that constitutive reduction in BMP signal by BMPRII mutations may cause abnormal vascular remodeling by promoting dedifferentiation of vascular smooth muscle cells (vSMCs). Here, we demonstrate that infusion of the amiloride analog phenamil during chronic-hypoxia treatment in rat attenuates development of PAH and vascular remodeling. Phenamil induces Tribbles homolog 3 (Trb3), a positive modulator of the BMP pathway that acts by stabilizing the Smad family signal transducers. Through induction of Trb3, phenamil promotes the differentiated, contractile vSMC phenotype characterized by elevated expression of contractile genes and reduced cell growth and migration. Phenamil activates the Trb3 gene transcription via activation of the calcium-calcineurin-nuclear factor of activated T cell (NFAT) pathway. These results indicate that constitutive elevation of Trb3 by phenamil is a potential therapy for IPAH and FPAH.

Requirement of TCF7L2 for TGF-beta-dependent transcriptional activation of the TMEPAI gene

The TGF-β and Wnt pathways are involved in cell fate and tumorigenicity. A recent report indicated that a TGF-β target gene, TMEPAI (transmembrane prostate androgen-induced RNA), is possibly also a downstream target of Wnt signaling. Although TMEPAI was believed to be involved in tumorigenicity because of its blockage of TGF-β signaling, how TGF-β and Wnt signals affect the activation of the TMEPAI gene is not well understood. Herein, we show that the TMEPAI promoter is regulated synergistically by TGF-β/Smad and Wnt/β-catenin/T cell factor (TCF) 7L2. The critical cis-element for dual signals, termed TGF-β-responsive TCF7L2-binding element (TTE), is located in intron 1 of the TMEPAI gene. TCF7L2, but not Smad proteins, bound to TTE, whereas the disruption of TTE by mutagenesis remarkably counteracted both TGF-β and TCF7L2 responses. The introduction of mutations in critical Smad-binding elements blocked the activation of the TMEPAI promoter by TCF7L2. Furthermore, our DNA-protein interaction experiments revealed the indirect binding of TCF7L2 to Smad-binding elements via Smad3 upon TGF-β stimulation as well as its TGF-β-dependent association with TTE. We demonstrate that the Wnt/β-catenin/TCF7L2 pathway is preferentially able to alter the transcriptional regulation of the TGF-β-target gene, TMEPAI.

Linking actin dynamics and gene transcription to drive cellular motile functions

Numerous physiological and pathological stimuli promote the rearrangement of the actin cytoskeleton, thereby modulating cellular motile functions. Although it seems intuitively obvious that cell motility requires coordinated protein biosynthesis, until recently the linkage between cytoskeletal actin dynamics and correlated gene activities remained unknown. This knowledge gap was filled in part by the discovery that globular actin polymerization liberates myocardin-related transcription factor (MRTF) cofactors, thereby inducing the nuclear transcription factor serum response factor (SRF) to modulate the expression of genes encoding structural and regulatory effectors of actin dynamics. This insight stimulated research to better understand the actin-MRTF-SRF circuit and to identify alternative mechanisms that link cytoskeletal dynamics and genome activity.

Deletion of the FHL2 gene attenuates the formation of atherosclerotic lesions after a cholesterol-enriched diet

AIMS

FHL2, a member of the four and a half LIM domain (FHL) family of proteins, may play an important role in the circulatory system and in particular atherosclerosis.

MAIN METHODS

To investigate the role of FHL2 in atherogenesis, FHL2-null and wild-type control male mice were fed either a normal chow (NC) or a cholesterol-enriched diet (CED).

KEY FINDINGS

At 3 months post CED, aortic atherosclerotic plaques were observed in both control and FHL2-null mice. Lesions in control mice increased dramatically by 6 months of CED. In contrast, lesion size did not increase during this time in CED-fed FHL2-null mice. Relative to control mice on a normal chow of diet (NCD), control mice on a CED exhibited lower circulating nitric oxide (NO) levels, and decreased expression of connexin37 (Cx37) and Cx40 in aortic endothelium. In contrast, FHL2-null mice on a CED maintained similar levels of circulating NO as FHL2-null mice fed a NCD. Cxs levels in aortic endothelium of FHL2-null mutants on a NCD were lower relative to control mice on a NCD, and did not decrease with CED.

SIGNIFICANCE

Our data demonstrate a role for FHL2 in atherogenesis, the regulation of circular NO release, and expression of gap junctions within aortic endothelium.

Molecular basis for antagonism between PDGF and the TGFbeta family of signalling pathways by control of miR-24 expression

Modulation of the vascular smooth-muscle-cell (vSMC) phenotype from a quiescent 'contractile' phenotype to a proliferative 'synthetic' phenotype has been implicated in vascular injury repair, as well as pathogenesis of vascular proliferative diseases. Both bone morphogenetic protein (BMP) and transforming growth factor-beta (TGFbeta)-signalling pathways promote a contractile phenotype, while the platelet-derived growth factor-BB (PDGF-BB)-signalling pathway promotes a switch to the synthetic phenotype. Here we show that PDGF-BB induces microRNA-24 (miR-24), which in turn leads to downregulation of Tribbles-like protein-3 (Trb3). Repression of Trb3 coincides with reduced expression of Smad proteins and decrease in BMP and TGFbeta signalling, promoting a synthetic phenotype in vSMCs. Inhibition of miR-24 by antisense oligonuclotides abrogates the downregulation of Trb3 as well as pro-synthetic activity of the PDGF-signalling pathway. Thus, this study provides a molecular basis for the antagonism between the PDGF and TGFbeta pathways, and its effect on the control of the vSMC phenotype.