Role of serum response factor in the pathogenesis of disease

Direct hybridization and bioinformatics analysis of circulating microRNAs in patients with Alzheimer's disease under intravenous trehalose treatment

Trehalose has been proposed as a possible therapeutic option for attenuating the neuropathological changes associated with neurodegeneration, including Alzheimer's disease (AD). The administration of trehalose in human and murine models was linked to restoring antioxidant status, decreasing lipoperoxidation, and alleviating neuroinflammation. This latter biochemical mechanism was associated with the upregulation of specific brain-enriched microRNAs (miRNA). Herein, using a direct hybridization approach, we evaluate trehalose intravenous treatment in AD patients, conducting a phase two clinical trial (IRCT20130829014521N15) examining the alteration of microRNA profiles before and after the treatment. Twenty patients were recruited and randomly assigned to two groups: the intervention group received 15 g/week of intravenous trehalose. The control group received placebo in the form of normal saline. The period chosen was 12 weeks. Blood samples were obtained at the beginning and end of the study. Circulating microRNAs expression data between the placebo and treatment groups were assessed using microarray analysis. Subsequently, differentially expressed (DE) miRNAs specific to the trehalose-treated group were identified, and their gene targets were determined by bioinformatics-based approaches. The analysis of DE miRNAs pointed out modulation in unique miRNAs between treatment and placebo groups. Specifically, hsa-miR-1268a, -3605-3p, -555, and -6511a-3p were significantly downregulated, while hsa-miR-324-3p and -539-5p showed significant upregulation. Of the 147 overlapped validated genes identified in the bioinformatics analysis, several are related to autophagy, protein aggregation, oxidative stress, and inflammation. KEGG enrichment pathways reveal regulation of actin cytoskeleton, axon guidance, and neurotrophin signaling pathways. The results identify significant modulation in unique miRNAs in AD patients under trehalose. These findings suggest the potential utility of these microRNAs as biomarkers for trehalose pharmacological monitoring in AD.

Cardiac-specific overexpression of serum response factor regulates age-associated decline in mitochondrial function

Cardiac aging is an intrinsic process that leads to impaired heart function, along with cellular and molecular changes. Recent research highlights the important role of mitochondria in cardiac function, due to the heart's high energy demands. Serum response factor (SRF), a transcription factor involved in regulating actin and smooth muscle gene expression, is well known as a regulator of various aspects of cardiac function. However, its role in mitochondrial regulation and cardiac aging is poorly understood. Our laboratory generated a transgenic mouse model with cardiac-specific overexpression of SRF, which exhibits characteristics of diastolic dysfunction and accelerated cardiac aging in young adult transgenic mice. In this study, we tested how cardiac-specific overexpression of SRF affects age associated mitochondrial dysfunction in the heart. Our results showed that cardiac specific SRF overexpression reduced the lifespan of mice and induced cardiomyopathy. Histological analysis revealed cardiac hypertrophy and fibrosis in transgenic mice hearts. SRF overexpression led to significant alterations in mitochondrial structure and function, including reduced mitochondrial biogenesis and dysregulation of oxidative phosphorylation. These changes were accompanied by increased oxidative stress, a decline in antioxidant enzyme activity, and disrupted calcium handling. Moreover, cardiac-specific SRF overexpression activated the MAPK signaling pathway. Our findings were further corroborated by similar mitochondrial dysfunction observed in a human cardiomyocyte cells transfected with SRF plasmid. Taken together, these findings suggest that SRF plays a novel role in cardiac aging, thus establishing SRF as a potential therapeutic target for mitigating age-associated decline in mitochondrial function and preserving cardiac health in older adults.

Single-molecule analysis reveals that IPMK enhances the DNA-binding activity of the transcription factor SRF

Serum response factor (SRF) is a master transcription factor that regulates immediate early genes and cytoskeletal remodeling genes. Despite its importance, the mechanisms through which SRF stably associates with its cognate promoter remain unknown. Our biochemical and protein-induced fluorescence enhancement analyses showed that the binding of SRF to serum response element was significantly increased by inositol polyphosphate multikinase (IPMK), an SRF cofactor. Moreover, real-time tracking of SRF loci in live cell nuclei demonstrated that the chromatin residence time of SRF was reduced by IPMK depletion in fibroblasts. Conversely, elevated IPMK levels extended the SRF-chromatin association. We identified that IPMK binds to the intrinsically disordered region of SRF, which is required for the IPMK-induced stable interaction of SRF with DNA. IPMK-mediated conformational changes in SRF were observed by single-molecule fluorescence resonance energy transfer assays. Therefore, our findings demonstrate that IPMK is a critical factor for promoting high-affinity SRF-chromatin association and provide insights into the mechanisms of SRF-dependent transcription control via chaperone-like activity.

Electrical Forces Improve Memory in Old Age

This penultimate chapter is based on a single paper published in Nature in 2022. I have used it specifically as an exemplar, in this case to show that memory improvement in old age may be regulated by a multiplicity of electrical forces. However, I include it because I believe that one could pick almost any other substantial single paper and show that a completely disparate set of biological mechanisms similarly depend crucially on multiple electrical forces.

New insights into the pharmacological inhibition of SRF activity: Key inhibitory targets and mechanisms

Serum Response Factor (SRF) is a critical regulatory transcription factor widely expressed across cell types and is essential for animal survival. Excessive SRF activity has been linked to various pathological conditions and diseases, including cardiovascular diseases, cancers and neurodegenerative disorders, making the inhibition of SRF hyperactivity a promising therapeutic strategy. This review summarizes recent advancements in the discovery and development of SRF inhibitors, their regulatory mechanisms, and their respective molecular foundations. These insights deepen our understanding of current therapeutic potentials, paving the way for novel approaches to treat diseases associated with SRF hyperactivity.

SRF promotes long-range chromatin loop formation and stem cell pluripotency

Serum response factor (SRF) is a transcription factor essential for cell proliferation, differentiation, and migration and is required for primitive streak and mesoderm formation in the embryo. The canonical roles of SRF are mediated by a diverse set of context-dependent cofactors. Here, we show that SRF physically interacts with CTCF and cohesin subunits at topologically associating domain (TAD) boundaries and loop anchors. SRF promotes long-range chromatin loop formation and contributes to TAD insulation. In embryonic stem cells (ESCs), SRF associates with SOX2 and NANOG and contributes to the formation of three-dimensional (3D) pluripotency hubs. Our findings reveal additional roles of SRF in higher-order chromatin organization.

Recent advances in serum response factor posttranslational modifications and their therapeutic potential in cardiovascular and neurological diseases

Serum Response Factor (SRF) is a key regulatory transcription factor present in various cell types throughout the body, playing essential roles in cellular functions under physiological conditions. Mutations and abnormal expression of SRF have been linked to the development of various diseases and disorders. Recent evidence highlights that post-translational modifications (PTMs) are critical for regulating SRF function in different cell types and contribute to disease pathogenesis. Targeting SRF-related PTMs is emerging as a promising therapeutic approach for treating SRF-associated diseases. In this review, we summarize recent advances in understanding SRF PTMs and their underlying regulatory mechanisms. We also explore the implications of SRF-PTM in related cardiovascular and neurological diseases and their potential for therapeutic intervention. This information underscores the significance of SRF PTMs in both physiological and pathological contexts, enhancing our understanding of disease mechanisms and paving the way for the development of novel therapeutic strategies.

Serum Response Factor Expression in Excess Permits a Dual Contractile-Proliferative Phenotype of Airway Smooth Muscle

The transcription factors (TFs) MyoCD (myocardin) and Elk-1 (ETS Like-1 protein) competitively bind to SRF (serum response factor) and control myogenic- and mitogenic-related gene expression in smooth muscle, respectively. Their functions are therefore mutually inhibitory, which results in a contractile-versus-proliferative phenotype dichotomy. Airway smooth muscle cell (ASMC) phenotype alterations occur in various inflammatory airway diseases, promoting pathological remodeling and contributing to airflow obstruction. We characterized MyoCD and Elk-1 interactions and their roles in phenotype determination in human ASMCs. MyoCD overexpression in ASMCs increased smooth muscle gene expression, force generation, and partially restored the loss of smooth muscle protein associated with prolonged culturing while inhibiting Elk-1 transcriptional activities and proliferation induced by EGF (epidermal growth factor). However, MyoCD overexpression failed to suppress these responses induced by FBS, as FBS also upregulated SRF expression to a degree that allowed unopposed function of both TFs. Inhibition of the RhoA pathway reversed said SRF changes, allowing inhibition of Elk-1 by MyoCD overexpression and suppressing FBS-mediated contractile protein gene upregulation. Our study confirmed that MyoCD in increased abundance can competitively inhibit Elk-1 function. However, SRF upregulation permits a dual contractile-proliferative ASMC phenotype that is anticipated to exacerbate pathological alterations, whereas therapies targeting SRF may inhibit pathological ASMC proliferation and contractile protein gene expression.

Nattokinase attenuates endothelial inflammation through the activation of SRF and THBS1

Natto contains a potent fibrinolytic enzyme called nattokinase (NK), which has thrombolytic, antihypertensive, antiatherosclerotic and lipid-lowering effects. Although NK has been recognized for its beneficial effect on humans with atherosclerotic cardiovascular disease (ASCVD), the underlying mechanisms involved in vascular inflammation-atherosclerosis development remain largely unknown. The current study aimed to explore the effects of NK on gene regulation, autophagy, necroptosis and inflammasome in vascular inflammation. The transcriptional profiles of NK in endothelial cells (ECs) by RNA sequencing (RNA-seq) revealed that NK affected THBS1, SRF and SREBF1 mRNA expression. In Q-PCR analysis, SRF and THBS1 were upregulated but SREBF1 was unaffected in ECs treated with NK. NK treatment induced autophagy and inhibited NLRP3 inflammasome and necroptosis in ECs. Furthermore, the inhibition of SRF or THBS1 by siRNA suppressed autophagy and enhanced the NLRP3 inflammasome and necroptosis. In a mouse model, NK reduced vascular inflammation by activating autophagy and inhibiting NLRP3 inflammasome and necroptosis. Our findings provide the first evidence that NK upregulates SRF and THBS1 genes, subsequently increasing autophagy and decreasing necroptosis and NLRP3 inflammasome formation to reduce vascular inflammation. Therefore, NK could serve as nutraceuticals or adjuvant therapies to reduce vascular inflammation and possible atherosclerosis progression.

Defining a Haplotype Encompassing the LCORL-NCAPG Locus Associated with Increased Lean Growth in Beef Cattle

Numerous studies have shown genetic variation at the LCORL-NCAPG locus is strongly associated with growth traits in beef cattle. However, a causative molecular variant has yet to be identified. To define all possible candidate variants, 34 Charolais-sired calves were whole-genome sequenced, including 17 homozygous for a long-range haplotype associated with increased growth (QQ) and 17 homozygous for potential ancestral haplotypes for this region (qq). The Q haplotype was refined to an 814 kb region between chr6:37,199,897-38,014,080 and contained 218 variants not found in qq individuals. These variants include an insertion in an intron of NCAPG, a previously documented mutation in NCAPG (rs109570900), two coding sequence mutations in LCORL (rs109696064 and rs384548488), and 15 variants located within ATAC peaks that were predicted to affect transcription factor binding. Notably, rs384548488 is a frameshift variant likely resulting in loss of function for long isoforms of LCORL. To test the association of the coding sequence variants of LCORL with phenotype, 405 cattle from five populations were genotyped. The two variants were in complete linkage disequilibrium. Statistical analysis of the three populations that contained QQ animals revealed significant (p < 0.05) associations with genotype and birth weight, live weight, carcass weight, hip height, and average daily gain. These findings affirm the link between this locus and growth in beef cattle and describe DNA variants that define the haplotype. However, further studies will be required to define the true causative mutation.

SM22α deficiency: promoting vascular fibrosis via SRF-SMAD3-mediated activation of Col1a2 transcription following arterial injury

Vascular fibrosis, characterized by increased Type I collagen expression, significantly contributes to vascular remodeling. Our previous studies show that disrupting the expression of SM22α (aka SM22, Tagln) induces extensive vascular remodeling following arterial injury, involving oxidative stress, inflammation, and chondrogenesis within the vessel wall. This study aims to investigate the molecular mechanisms underlying the transcription of Col1a2 , a key fibrotic extracellular matrix marker. We observed upregulation of COL1A2 in the arterial wall of Sm22 -/- mice following carotid injury. Bioinformatics and molecular analyses reveal that Col1a2 transcription depends on a CArG box in the promoter, activated synergistically by SRF and SMAD3. Notably, we detected enhanced nuclear translocation of both SRF and SMAD3 in the smooth muscle cells of the injured carotid artery in Sm22 -/- mice. These findings demonstrate that SM22 deficiency regulates vascular fibrosis through the interaction of SRF and the SMAD3-mediated canonical TGF-β1 signal pathway, suggesting SM22α as a potential therapeutic target for preventing vascular fibrosis.

Serum response factor promoting axonal regeneration by activating the Ras-Raf-Cofilin signaling pathway after the spinal cord injury

INTRODUCTION

Serum response factor (SRF) is important in muscle development, tissue repair, and neuronal regulation.

OBJECTIVES

This research aims to thoroughly examine the effects of SRF on spinal cord injury (SCI) and its ability to significantly impact the recovery and regeneration of neuronal axons.

METHODS

The researchers created rat models of SCI and scratch injury to primary spinal cord neurons to observe the expression of relevant factors after neuronal injury.

RESULTS

We found that the SRF, Ras, Raf, and cofilin levels increased after injury and gradually returned to normal levels. Afterward, researchers gave rats with SCI an SRF inhibitor (CCG1423) and studied the effects with nuclear magnetic resonance and transmission electron microscopy. The SRF inhibitor rodents had worse spinal cord recovery and axon regrowth than the control group. And the apoptosis of primary neurons after scratch injury was significantly higher in the SRF inhibitor group. Additionally, the researchers utilized lentiviral transfection to modify the SRF expression in neurons. SRF overexpression increased neuron migration while silencing SRF decreased it. Finally, Western blotting and RT-PCR were conducted to examine the expression changes of related factors upon altering SRF expression. The results revealed SRF overexpression increased Ras, Raf, and cofilin expression. Silencing SRF decreased Ras, Raf, and Cofilin expression.

CONCLUSION

Based on our research, the SRF promotes axonal regeneration by activating the "Ras-Raf-Cofilin" signaling pathway.

The lysine methyltransferase SMYD2 facilitates neointimal hyperplasia by regulating the HDAC3-SRF axis

Coronary restenosis is an important cause of poor long-term prognosis in patients with coronary heart disease. Here, we show that lysine methyltransferase SMYD2 expression in the nucleus is significantly elevated in serum- and PDGF-BB-induced vascular smooth muscle cells (VSMCs), and in tissues of carotid artery injury-induced neointimal hyperplasia. Smyd2 overexpression in VSMCs (Smyd2-vTg) facilitates, but treatment with its specific inhibitor LLY-507 or SMYD2 knockdown significantly inhibits VSMC phenotypic switching and carotid artery injury-induced neointima formation in mice. Transcriptome sequencing revealed that SMYD2 knockdown represses the expression of serum response factor (SRF) target genes and that SRF overexpression largely reverses the inhibitory effect of SMYD2 knockdown on VSMC proliferation. HDAC3 directly interacts with and deacetylates SRF, which enhances SRF transcriptional activity in VSMCs. Moreover, SMYD2 promotes HDAC3 expression via tri-methylation of H3K36 at its promoter. RGFP966, a specific inhibitor of HDAC3, not only counteracts the pro-proliferation effect of SMYD2 overexpression on VSMCs, but also inhibits carotid artery injury-induced neointima formation in mice. HDAC3 partially abolishes the inhibitory effect of SMYD2 knockdown on VSMC proliferation in a deacetylase activity-dependent manner. Our results reveal that the SMYD2-HDAC3-SRF axis constitutes a novel and critical epigenetic mechanism that regulates VSMC phenotypic switching and neointimal hyperplasia.

DNA Conserved in Diverse Animals Since the Precambrian Controls Genes for Embryonic Development

DNA that controls gene expression (e.g. enhancers, promoters) has seemed almost never to be conserved between distantly related animals, like vertebrates and arthropods. This is mysterious, because development of such animals is partly organized by homologous genes with similar complex expression patterns, termed "deep homology." Here, we report 25 regulatory DNA segments conserved across bilaterian animals, of which 7 are also conserved in cnidaria (coral and sea anemone). They control developmental genes (e.g. Nr2f, Ptch, Rfx1/3, Sall, Smad6, Sp5, Tbx2/3), including six homeobox genes: Gsx, Hmx, Meis, Msx, Six1/2, and Zfhx3/4. The segments contain perfectly or near-perfectly conserved CCAAT boxes, E-boxes, and other sequences recognized by regulatory proteins. More such DNA conservation will surely be found soon, as more genomes are published and sequence comparison is optimized. This reveals a control system for animal development conserved since the Precambrian.

Tissue-specific Cre driver mice to study vascular diseases

Vascular diseases, including atherosclerosis and abdominal aneurysms, are the primary cause of mortality and morbidity among the elderly worldwide. The life quality of patients is significantly compromised due to inadequate therapeutic approaches and limited drug targets. To expand our comprehension of vascular diseases, gene knockout (KO) mice, especially conditional knockout (cKO) mice, are widely used for investigating gene function and mechanisms of action. The Cre-loxP system is the most common method for generating cKO mice. Numerous Cre driver mice have been established to study the main cell types that compose blood vessels, including endothelial cells, smooth muscle cells, and fibroblasts. Here, we first discuss the characteristics of each layer of the arterial wall. Next, we provide an overview of the representative Cre driver mice utilized for each of the major cell types in the vessel wall and their most recent applications in vascular biology. We then go over Cre toxicity and discuss the practical methods for minimizing Cre interference in experimental outcomes. Finally, we look into the future of tissue-specific Cre drivers by introducing the revolutionary single-cell RNA sequencing and dual recombinase system.

Unraveling temporal and spatial biomarkers of epithelial-mesenchymal transition in colorectal cancer: insights into the crucial role of immunosuppressive cells

The occurrence and progression of tumors can be established through a complex interplay among tumor cells undergoing epithelial-mesenchymal transition (EMT), invasive factors and immune cells. In this study, we employed single-cell RNA sequencing (scRNA-seq) and spatially resolved transcriptomics (ST) to evaluate the pseudotime trajectory and spatial interactive relationship between EMT-invasive malignant tumors and immune cells in primary colorectal cancer (CRC) tissues at different stages (stage I/II and stage III with tumor deposit). Our research characterized the spatiotemporal relationship among different invasive tumor programs by constructing pseudotime endpoint-EMT-invasion tumor programs (EMTPs) located at the edge of ST, utilizing evolution trajectory analysis integrated with EMT-invasion genes. Strikingly, the invasive and expansive process of tumors undergoes remarkable spatial reprogramming of regulatory and immunosuppressive cells, such as myeloid-derived suppressor cells (MDSCs), tumor-associated macrophages (TAMs), regulatory T cells (Treg), and exhausted T cells (Tex). These EMTP-adjacent cell are linked to EMT-related invasion genes, especially the C-X-C motif ligand 1 (CXCL1) and CXCL8 genes that are important for CRC prognosis. Interestingly, the EMTPs in stage I mainly produce an inflammatory margin invasive niche, while the EMTPs in stage III tissues likely produce a hypoxic pre-invasive niche. Our data demonstrate the crucial role of regulatory and immunosuppressive cells in tumor formation and progression of CRC. This study provides a framework to delineate the spatiotemporal invasive niche in CRC samples.

Cellular signaling modulated by miRNA-3652 in ovarian cancer: unveiling mechanistic pathways for future therapeutic strategies

MicroRNAs (miRNAs) are small non-coding RNA molecules that play pivotal roles in regulating gene expression and have been implicated in the pathogenesis of numerous cancers. miRNA-3652, though relatively less explored, has recently emerged as a potential key player in ovarian cancer's molecular landscape. This review aims to delineate the functional significance and tumor progression role of miRNA-3652 in ovarian cancer, shedding light on its potential as both a diagnostic biomarker and therapeutic target. A comprehensive literature search was carried out using established databases, the focus was on articles that reported the role of miRNA-3652 in ovarian cancer, encompassing mechanistic insights, functional studies, and its association with clinical outcomes. This updated review highlighted that miRNA-3652 is intricately involved in ovarian cancer cell proliferation, migration, and invasion, its dysregulation was linked to altered expression of critical genes involved in tumor growth and metastasis; furthermore, miRNA-3652 expression levels were found to correlate with clinical stages, prognosis, and response to therapy in ovarian cancer patients. miRNA-3652 holds significant promise as a vital molecular player in ovarian cancer's pathophysiology. Its functional role and impact on tumor progression make it a potential candidate for diagnostic and therapeutic applications in ovarian cancer. Given the pivotal role of miRNA-3652 in ovarian cancer, future studies should emphasize in-depth mechanistic explorations, utilizing advanced genomic and proteomic tools. Collaboration between basic scientists and clinicians will be vital to translating these findings into innovative diagnostic and therapeutic strategies, ultimately benefiting ovarian cancer patients. Video Abstract.

Aberrations in Energetic Metabolism and Stress-Related Pathways Contribute to Pathophysiology in the Neb Conditional Knockout Mouse Model of Nemaline Myopathy

Nemaline myopathy (NM) is a genetically and clinically heterogeneous disease that is diagnosed on the basis of the presence of nemaline rods on skeletal muscle biopsy. Although NM has typically been classified by causative genes, disease severity or prognosis cannot be predicted. The common pathologic end point of nemaline rods (despite diverse genetic causes) and an unexplained range of muscle weakness suggest that shared secondary processes contribute to the pathogenesis of NM. We speculated that these processes could be identified through a proteome-wide interrogation using a mouse model of severe NM in combination with pathway validation and structural/functional analyses. A proteomic analysis was performed using skeletal muscle tissue from the Neb conditional knockout mouse model compared with its wild-type counterpart to identify pathophysiologically relevant biological processes that might impact disease severity or provide new treatment targets. A differential expression analysis and Ingenuity Pathway Core Analysis predicted perturbations in several cellular processes, including mitochondrial dysfunction and changes in energetic metabolism and stress-related pathways. Subsequent structural and functional studies demonstrated abnormal mitochondrial distribution, decreased mitochondrial respiratory function, an increase in mitochondrial transmembrane potential, and extremely low ATP content in Neb conditional knockout muscles relative to wild type. Overall, the findings of these studies support a role for severe mitochondrial dysfunction as a novel contributor to muscle weakness in NM.

Identification of key lipid metabolism-related genes in Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) represents profound degenerative conditions of the brain that cause significant deterioration in memory and cognitive function. Despite extensive research on the significant contribution of lipid metabolism to AD progression, the precise mechanisms remain incompletely understood. Hence, this study aimed to identify key differentially expressed lipid metabolism-related genes (DELMRGs) in AD progression.

METHODS

Comprehensive analyses were performed to determine key DELMRGs in AD compared to controls in GSE122063 dataset from Gene Expression Omnibus. Additionally, the ssGSEA algorithm was utilized for estimating immune cell levels. Subsequently, correlations between key DELMRGs and each immune cell were calculated specifically in AD samples. The key DELMRGs expression levels were validated via two external datasets. Furthermore, gene set enrichment analysis (GSEA) was utilized for deriving associated pathways of key DELMRGs. Additionally, miRNA-TF regulatory networks of the key DELMRGs were constructed using the miRDB, NetworkAnalyst 3.0, and Cytoscape software. Finally, based on key DELMRGs, AD samples were further segmented into two subclusters via consensus clustering, and immune cell patterns and pathway differences between the two subclusters were examined.

RESULTS

Seventy up-regulated and 100 down-regulated DELMRGs were identified. Subsequently, three key DELMRGs (DLD, PLPP2, and PLAAT4) were determined utilizing three algorithms [(i) LASSO, (ii) SVM-RFE, and (iii) random forest]. Specifically, PLPP2 and PLAAT4 were up-regulated, while DLD exhibited downregulation in AD cerebral cortex tissue. This was validated in two separate external datasets (GSE132903 and GSE33000). The AD group exhibited significantly altered immune cell composition compared to controls. In addition, GSEA identified various pathways commonly associated with three key DELMRGs. Moreover, the regulatory network of miRNA-TF for key DELMRGs was established. Finally, significant differences in immune cell levels and several pathways were identified between the two subclusters.

CONCLUSION

This study identified DLD, PLPP2, and PLAAT4 as key DELMRGs in AD progression, providing novel insights for AD prevention/treatment.

Transcription factor 21 accelerates vascular calcification in mice by activating the IL-6/STAT3 signaling pathway and the interplay between VSMCs and ECs

Vascular calcification is caused by the deposition of calcium salts in the intimal or tunica media layer of the aorta, which increases the risk of cardiovascular events and all-cause mortality. However, the mechanisms underlying vascular calcification are not fully clarified. Recently it has been shown that transcription factor 21 (TCF21) is highly expressed in human and mouse atherosclerotic plaques. In this study we investigated the role of TCF21 in vascular calcification and the underlying mechanisms. In carotid artery atherosclerotic plaques collected from 6 patients, we found that TCF21 expression was upregulated in calcific areas. We further demonstrated TCF21 expression was increased in an in vitro vascular smooth muscle cell (VSMC) osteogenesis model. TCF21 overexpression promoted osteogenic differentiation of VSMC, whereas TCF21 knockdown in VSMC attenuated the calcification. Similar results were observed in ex vivo mouse thoracic aorta rings. Previous reports showed that TCF21 bound to myocardin (MYOCD) to inhibit the transcriptional activity of serum response factor (SRF)-MYOCD complex. We found that SRF overexpression significantly attenuated TCF21-induced VSMC and aortic ring calcification. Overexpression of SRF, but not MYOCD, reversed TCF21-inhibited expression of contractile genes SMA and SM22. More importantly, under high inorganic phosphate (3 mM) condition, SRF overexpression reduced TCF21-induced expression of calcification-related genes (BMP2 and RUNX2) as well as vascular calcification. Moreover, TCF21 overexpression enhanced IL-6 expression and downstream STAT3 activation to facilitate vascular calcification. Both LPS and STAT3 could induce TCF21 expression, suggesting that the inflammation and TCF21 might form a positive feedback loop to amplify the activation of IL-6/STAT3 signaling pathway. On the other hand, TCF21 induced production of inflammatory cytokines IL-1β and IL-6 in endothelial cells (ECs) to promote VSMC osteogenesis. In EC-specific TCF21 knockout (TCF21ECKO) mice, VD3 and nicotine-induced vascular calcification was significantly reduced. Our results suggest that TCF21 aggravates vascular calcification by activating IL-6/STAT3 signaling and interplay between VSMC and EC, which provides new insights into the pathogenesis of vascular calcification. TCF21 enhances vascular calcification by activating the IL-6-STAT3 signaling pathway. TCF21 inhibition may be a new potential therapeutic strategy for the prevention and treatment of vascular calcification.

Hepatocellular carcinoma: The virus or the liver?

Hepatocellular carcinoma (HCC) represents a major public health problem being one of the most common causes of cancer-related deaths worldwide. Hepatitis B (HBV) and C viruses have been classified as oncoviruses and are responsible for the majority of HCC cases, while the role of hepatitis D virus (HDV) in liver carcinogenesis has not been elucidated. HDV/HBV coinfection is related to more severe liver damage than HBV mono-infection and recent studies suggest that HDV/HBV patients are at increased risk of developing HCC compared to HBV mono-infected patients. HBV is known to promote hepatocarcinogenesis via DNA integration into host DNA, disruption of molecular pathways by regulatory HBV x (HBx) protein and excessive oxidative stress. Recently, several molecular mechanisms have been proposed to clarify the pathogenesis of HDV-related HCC including activation of signalling pathways by specific HDV antigens, epigenetic dysregulation and altered gene expression. Alongside, ongoing chronic inflammation and impaired immune responses have also been suggested to facilitate carcinogenesis. Finally, cellular senescence seems to play an important role in chronic viral infection and inflammation leading to hepatocarcinogenesis. In this review, we summarize the current literature on the impact of HDV in HCC development and discuss the potential interplay between HBV, HDV and neighbouring liver tissue in liver carcinogenesis.

An integrated mechanistic and data-driven computational model predicts cell responses to high- and low-affinity EGFR ligands

The biophysical properties of ligand binding heavily influence the ability of receptors to specify cell fates. Understanding the rules by which ligand binding kinetics impact cell phenotype is challenging, however, because of the coupled information transfers that occur from receptors to downstream signaling effectors and from effectors to phenotypes. Here, we address that issue by developing an integrated mechanistic and data-driven computational modeling platform to predict cell responses to different ligands for the epidermal growth factor receptor (EGFR). Experimental data for model training and validation were generated using MCF7 human breast cancer cells treated with the high- and low-affinity ligands epidermal growth factor (EGF) and epiregulin (EREG), respectively. The integrated model captures the unintuitive, concentration-dependent abilities of EGF and EREG to drive signals and phenotypes differently, even at similar levels of receptor occupancy. For example, the model correctly predicts the dominance of EREG over EGF in driving a cell differentiation phenotype through AKT signaling at intermediate and saturating ligand concentrations and the ability of EGF and EREG to drive a broadly concentration-sensitive migration phenotype through cooperative ERK and AKT signaling. Parameter sensitivity analysis identifies EGFR endocytosis, which is differentially regulated by EGF and EREG, as one of the most important determinants of the alternative phenotypes driven by different ligands. The integrated model provides a new platform to predict how phenotypes are controlled by the earliest biophysical rate processes in signal transduction and may eventually be leveraged to understand receptor signaling system performance depends on cell context.

One-sentence summary

Integrated kinetic and data-driven EGFR signaling model identifies the specific signaling mechanisms that dictate cell responses to EGFR activation by different ligands.

Serum response factor activates peroxidasin transcription to block senescence of hepatic stellate cells

AIMS

Aberrant liver fibrosis is a hallmark event in end-stage liver diseases. Hepatic stellate cells (HSCs) are considered the major source of myofibroblasts in the liver that produce extracellular matrix proteins to promote liver fibrosis. HSCs undergo senescence in response to various stimuli, a process that can be exploited to dampen liver fibrosis. We investigated the role of serum response factor (SRF) in this process.

METHODS AND MATERIALS

Senescence was induced HSCs by serum withdrawal or progressive passage. DNA-protein interaction was evaluated by chromatin immunoprecipitation (ChIP).

RESULTS

SRF expression was down-regulated in HSCs entering into senescence. Coincidently, SRF depletion by RNAi accelerated HSC senescence. Of note, treatment of an anti-oxidant (N-acetylcysteine or NAC) blocked HSC senescence by SRF deficiency suggesting that SRF may antagonize HSC senescence by eliminating excessive reactive oxygen species (ROS). PCR-array based screening identified peroxidasin (PXDN) as a potential target for SRF in HSCs. PXDN expression was inversely correlated with HSC senescence whereas PXDN knockdown accelerated HSC senescence. Further analysis reveals that SRF directly bound to the PXDN promoter and activated PXDN transcription. Consistently, PXDN over-expression protected whereas PXDN depletion amplified HSC senescence. Finally, PXDN knockout mice displayed diminished liver fibrosis compared to wild type mice when subjected to bile duct ligation (BDL).

SIGNIFICANCE

Our data suggest that SRF, via its downstream target PXDN, plays a key role in regulating HSC senescence.

Base-resolution UV footprinting by sequencing reveals distinctive damage signatures for DNA-binding proteins

Decades ago, it was shown that proteins binding to DNA can quantitatively alter the formation of DNA damage by UV light. This established the principle of UV footprinting for non-intrusive study of protein-DNA contacts in living cells, albeit at limited scale and precision. Here, we perform deep base-resolution quantification of the principal UV damage lesion, the cyclobutane pyrimidine dimer (CPD), at select human promoter regions using targeted CPD sequencing. Several transcription factors exhibited distinctive and repeatable damage signatures indicative of site occupancy, involving strong (up to 17-fold) position-specific elevations and reductions in CPD formation frequency relative to naked DNA. Positive damage modulation at some ETS transcription factor binding sites coincided at base level with melanoma somatic mutation hotspots. Our work provides proof of concept for the study of protein-DNA interactions at individual loci using light and sequencing, and reveals widespread and potent modulation of UV damage in regulatory regions.

G protein-coupled receptors in neurodegenerative diseases and psychiatric disorders

Neuropsychiatric disorders are multifactorial disorders with diverse aetiological factors. Identifying treatment targets is challenging because the diseases are resulting from heterogeneous biological, genetic, and environmental factors. Nevertheless, the increasing understanding of G protein-coupled receptor (GPCR) opens a new possibility in drug discovery. Harnessing our knowledge of molecular mechanisms and structural information of GPCRs will be advantageous for developing effective drugs. This review provides an overview of the role of GPCRs in various neurodegenerative and psychiatric diseases. Besides, we highlight the emerging opportunities of novel GPCR targets and address recent progress in GPCR drug development.

The Involvement of Krüppel-like Factors in Cardiovascular Diseases

Krüppel-like factors (KLFs) are a set of DNA-binding proteins belonging to a family of zinc-finger transcription factors, which have been associated with many biological processes related to the activation or repression of genes, inducing cell growth, differentiation, and death, and the development and maintenance of tissues. In response to metabolic alterations caused by disease and stress, the heart will undergo cardiac remodeling, leading to cardiovascular diseases (CVDs). KLFs are among the transcriptional factors that take control of many physiological and, in this case, pathophysiological processes of CVD. KLFs seem to be associated with congenital heart disease-linked syndromes, malformations because of autosomal diseases, mutations that relate to protein instability, and/or loss of functions such as atheroprotective activities. Ischemic damage also relates to KLF dysregulation because of the differentiation of cardiac myofibroblasts or a modified fatty acid oxidation related to the formation of a dilated cardiomyopathy, myocardial infarctions, left ventricular hypertrophy, and diabetic cardiomyopathies. In this review, we describe the importance of KLFs in cardiovascular diseases such as atherosclerosis, myocardial infarction, left ventricle hypertrophy, stroke, diabetic cardiomyopathy, and congenital heart diseases. We further discuss microRNAs that have been involved in certain regulatory loops of KLFs as they may act as critical in CVDs.

TCF7L1 Accelerates Smooth Muscle Cell Phenotypic Switching and Aggravates Abdominal Aortic Aneurysms

Phenotypic switching of vascular smooth muscle cells is a central process in abdominal aortic aneurysm (AAA) pathology. We found that knockdown TCF7L1 (transcription factor 7-like 1), a member of the TCF/LEF (T cell factor/lymphoid enhancer factor) family of transcription factors, inhibits vascular smooth muscle cell differentiation. This study hints at potential interventions to maintain a normal, differentiated smooth muscle cell state, thereby eliminating the pathogenesis of AAA. In addition, our study provides insights into the potential use of TCF7L1 as a biomarker for AAA.

Physical inactivity by tail suspension alters markers of metabolism, structure, and autophagy of the mouse heart

Sedentary behavior has become ingrained in our society and has been linked to cardiovascular diseases. Physical inactivity is the main characteristic of sedentary behavior. However, its impact on cardiovascular disease is not clear. Therefore, we investigated the effect of physical inactivity in an established mouse model on gene clusters associated with cardiac fibrosis, electrophysiology, cell regeneration, and tissue degradation/turnover. We investigated a sedentary group (CTR, n = 10) versus a tail suspension group (TS, n = 11) that caused hindlimb unloading and consequently physical inactivity. Through histological, protein content, and transcript analysis approaches, we found that cardiac fibrosis-related genes partly change, with significant TS-associated increases in Tgfb1, but without changes in Col1a1 and Fn1. These changes are not translated into fibrosis at tissue level. We further detected TS-mediated increases in protein degradation- (Trim63, p < 0.001; Fbxo32, p = 0.0947 as well as in biosynthesis-related [P70s6kb1, p < 0.01]). Corroborating these results, we found increased expression of autophagy markers such as Atg7 (p < 0.01) and ULK1 (p < 0.05). Two cardiomyocyte regeneration- and sarcomerogenesis-related genes, Yap (p = 0.0535) and Srf (p < 0.001), increased upon TS compared to CTR conditions. Finally, we found significant upregulation of Gja1 (p < 0.05) and a significant downregulation of Aqp1 (p < 0.05). Our data demonstrate that merely 2 weeks of reduced physical activity induce changes in genes associated with cardiac structure and electrophysiology. Hence, these data should find the basis for novel research directed to evaluate the interplay of cardiac functioning and physical inactivity.

LPA maintains innate antiviral immunity in a pro-active state via STK38L-mediated IRF3 Ser303 phosphorylation

Innate immunity is critical for the early detection and elimination of viral invasion. Extracellular signals are crucial for host resistance; however, how extracellular factors prepare the innate immunity for rapid antiviral response remains elusive. Here, we find that serum deprivation largely restricts the innate antiviral responses to RNA and DNA viruses. When serum is supplied, serine/threonine-protein kinase 38-like (STK38L), induced by serum response factor (SRF), phosphorylates IRF3 at Ser303, which prevents IRF3 from proteasome-mediated degradation in the rest state (non-infected), and ensures that enough IRF3 is called in the primed state (infected). STK38L-deficient mice exhibit compromised innate antiviral responses and elevated viral proliferation and mortality. Moreover, lysophosphatidic acid (LPA) or sphingosine 1-phosphate (S1P), the crucial activators of SRF, rescue immunosuppression caused by serum deprivation. These findings identify the SRF-STK38L-IRF3 axis as a novel mechanism that maintains the host in a pro-active state when not infected, which ensures the rapid immune response against virus.

Inhibition of ANXA2 regulated by SRF attenuates the development of severe acute pancreatitis by inhibiting the NF-κB signaling pathway

BACKGROUND

Acute pancreatitis (AP) is an inflammatory process of the pancreas resulting from biliary obstruction or alcohol consumption. Approximately, 10-20% of AP can evolve into severe AP (SAP). In this study, we sought to explore the physiological roles of the transcription factor serum response factor (SRF), annexin A2 (ANXA2), and nuclear factor-kappaB (NF-κB) in SAP.

METHODS

C57BL/6 mice and rat pancreatic acinar cells (AR42J) were used to establish an AP model in vivo and in vitro by cerulein with or without lipopolysaccharide (LPS). Production of pro-inflammatory cytokines (IL-1β and TNF-α) were examined by ELISA and immunoblotting analysis. Hematoxylin and eosin (HE) staining and TUNEL staining were performed to evaluate pathological changes in the course of AP. Apoptosis was examined by flow cytometric and immunoblotting analysis. Molecular interactions were tested by dual luciferase reporter, ChIP, and Co-IP assays.

RESULTS

ANXA2 was overexpressed in AP and correlated to the severity of AP. ANXA2 knockdown rescued pancreatic acinar cells against inflammation and apoptosis induced by cerulein with or without LPS. Mechanistic investigations revealed that SRF bound with the ANXA2 promoter region and repressed its expression. ANXA2 could activate the NF-κB signaling pathway by inducing the nuclear translocation of p50. SRF-mediated transcriptional repression of ANXA2-protected pancreatic acinar cells against AP-like injury through repressing the NF-κB signaling pathway.

CONCLUSION

Our study highlighted a regulatory network consisting of SRF, ANXA2, and NF-κB that was involved in AP progression, possibly providing some novel targets for treating SAP.

Mechanism of histone deacetylases in cardiac hypertrophy and its therapeutic inhibitors

Cardiac hypertrophy is a key process in cardiac remodeling development, leading to ventricle enlargement and heart failure. Recently, studies show the complicated relation between cardiac hypertrophy and epigenetic modification. Post-translational modification of histone is an essential part of epigenetic modification, which is relevant to multiple cardiac diseases, especially in cardiac hypertrophy. There is a group of enzymes related in the balance of histone acetylation/deacetylation, which is defined as histone acetyltransferase (HAT) and histone deacetylase (HDAC). In this review, we introduce an important enzyme family HDAC, a key regulator in histone deacetylation. In cardiac hypertrophy HDAC I downregulates the anti-hypertrophy gene expression, including Kruppel-like factor 4 (Klf4) and inositol-5 phosphatase f (Inpp5f), and promote the development of cardiac hypertrophy. On the contrary, HDAC II binds to myocyte-specific enhancer factor 2 (MEF2), inhibit the assemble ability to HAT and protect against cardiac hypertrophy. Under adverse stimuli such as pressure overload and calcineurin stimulation, the HDAC II transfer to cytoplasm, and MEF2 can bind to nuclear factor of activated T cells (NFAT) or GATA binding protein 4 (GATA4), mediating inappropriate gene expression. HDAC III, also known as SIRTs, can interact not only to transcription factors, but also exist interaction mechanisms to other HDACs, such as HDAC IIa. We also present the latest progress of HDAC inhibitors (HDACi), as a potential treatment target in cardiac hypertrophy.

SRF in Neurochemistry: Overview of Recent Advances in Research on the Nervous System

Serum response factor (SRF) is a representative transcription factor that plays crucial roles in various biological phenomena by regulating immediate early genes (IEGs) and genes related to cell morphology and motility, among others. Over the years, the signal transduction pathways activating SRF have been clarified and SRF-target genes have been identified. In this overview, we initially briefly summarize the basic biology of SRF and its cofactors, ternary complex factor (TCF) and megakaryoblastic leukemia (MKL)/myocardin-related transcription factor (MRTF). Progress in the generation of nervous system-specific knockout (KO) or genetically modified mice as well as genetic analyses over the last few decades has not only identified novel SRF-target genes but also highlighted the neurochemical importance of SRF and its cofactors. Therefore, here we next present the phenotypes of mice with nervous system-specific KO of SRF or its cofactors by depicting recent findings associated with brain development, plasticity, epilepsy, stress response, and drug addiction, all of which result from function or dysfunction of the SRF axis. Last, we develop a hypothesis regarding the possible involvement of SRF and its cofactors in human neurological disorders including neurodegenerative, psychiatric, and neurodevelopmental diseases. This overview should deepen our understanding, highlight promising future directions for developing novel therapeutic strategies, and lead to illumination of the mechanisms underlying higher brain functions based on neuronal structure and function.

Old blood from heterochronic parabionts accelerates vascular aging in young mice: transcriptomic signature of pathologic smooth muscle remodeling

Vascular aging has a central role in the pathogenesis of cardiovascular diseases contributing to increased mortality of older adults. There is increasing evidence that, in addition to the documented role of cell-autonomous mechanisms of aging, cell-nonautonomous mechanisms also play a critical role in the regulation of vascular aging processes. Our recent transcriptomic studies (Kiss T. et al. Geroscience. 2020;42(2):727-748) demonstrated that circulating anti-geronic factors from young blood promote vascular rejuvenation in aged mice. The present study was designed to expand upon the results of this study by testing the hypothesis that circulating pro-geronic factors also contribute to the genesis of vascular aging phenotypes. To test this hypothesis, through heterochronic parabiosis, we determined the extent to which shifts in the vascular transcriptome (RNA-seq) are modulated by the old systemic environment. We reanalyzed existing RNA-seq data, comparing the transcriptome in the aorta arch samples isolated from isochronic parabiont aged (20-month-old) C57BL/6 mice [A-(A); parabiosis for 8 weeks] and young isochronic parabiont (6-month-old) mice [Y-(Y)] and also assessing transcriptomic changes in the aortic arch in young (6-month-old) parabiont mice [Y-(A); heterochronic parabiosis for 8 weeks] induced by the presence of old blood derived from aged (20-month-old) parabionts. We identified 528 concordant genes whose expression levels differed in the aged phenotype and were shifted towards the aged phenotype by the presence of old blood in young Y-(A) animals. Among them, the expression of 221 concordant genes was unaffected by the presence of young blood in A-(Y) mice. GO enrichment analysis suggests that old blood-regulated genes may contribute to pathologic vascular remodeling. IPA Upstream Regulator analysis (performed to identify upstream transcriptional regulators that may contribute to the observed transcriptomic changes) suggests that the mechanism of action of pro-geronic factors present in old blood may include inhibition of pathways mediated by SRF (serum response factor), insulin-like growth factor-1 (IGF-1) and VEGF-A. In conclusion, relatively short-term exposure to old blood can accelerate vascular aging processes. Our findings provide additional evidence supporting the significant plasticity of vascular aging and the existence of circulating pro-geronic factors mediating pathological remodeling of the vascular smooth muscle cells and the extracellular matrix.

Differential translational regulation of host exosomal proteins play key role in immunomodulation in antimony resistance in Visceral Leishmaniasis: A proteomic profiling study

In host-pathogen interactions, exosomal secretions are crucial for cell to cell communication and have an established role in immunomodulation. Protozoans, including Leishmania, modulates their host vesicular secretions for better survival; although the role of exosomal secretions in unresponsive against sodium antimony gluconate (SAG) has never been documented. In this study, the exosomal proteome of RAW macrophages infected with either SAG responsive (SAG^S) or SAG unresponsive (SAG^R) L. donovani parasites has been compared with uninfected RAW macrophages. Proteins isolated from exosomes were labelled with iTRAQ reagents; followed by subsequent LC-TOF/-MS analysis. In total, 394 proteins (p < 0.05) were identified which were shared common among all sets. Highly differentially expressed proteins were sorted by log2 value -1 and +1 as down regulated and up regulated respectively which yielded 58 proteins in SAG^R and 41 proteins during SAG^S infection. Out of the 58 proteins identified during SAG^R infection, 17 proteins were of immune modulatory function. Network visualization model and pathway analysis revealed the interactions among these proteins via different immunological pathways with reported involvement of some proteins in SAG resistance and host immune modulation. Hence, the differential abundance of immune pathway related proteins in exosomes of infected host during SAG^R infection supports the immune modulatory strategy adopted by SAG resistant parasites for enhanced survival .

SH3-Binding Glutamic Acid Rich-Deficiency Augments Apoptosis in Neonatal Rat Cardiomyocytes

Congenital heart disease (CHD) is one of the most common birth defects in humans, present in around 40% of newborns with Down’s syndrome (DS). The SH3 domain-binding glutamic acid-rich (SH3BGR) gene, which maps to the DS region, belongs to a gene family encoding a cluster of small thioredoxin-like proteins sharing SH3 domains. Although its expression is confined to the cardiac and skeletal muscle, the physiological role of SH3BGR in the heart is poorly understood. Interestingly, we observed a significant upregulation of SH3BGR in failing hearts of mice and human patients with hypertrophic cardiomyopathy. Along these lines, the overexpression of SH3BGR exhibited a significant increase in the expression of hypertrophic markers (Nppa and Nppb) and increased cell surface area in neonatal rat ventricular cardiomyocytes (NRVCMs), whereas its knockdown attenuated cellular hypertrophy. Mechanistically, using serum response factor (SRF) response element-driven luciferase assays in the presence or the absence of RhoA or its inhibitor, we found that the pro-hypertrophic effects of SH3BGR are mediated via the RhoA–SRF axis. Furthermore, SH3BGR knockdown resulted in the induction of apoptosis and reduced cell viability in NRVCMs via apoptotic Hippo–YAP signaling. Taking these results together, we here show that SH3BGR is vital for maintaining cytoskeletal integrity and cellular viability in NRVCMs through its modulation of the SRF/YAP signaling pathways.

A GSK3-SRF Axis Mediates Angiotensin II Induced Endothelin Transcription in Vascular Endothelial Cells

Endothelin, encoded by ET1, is a vasoactive substance primarily synthesized in vascular endothelial cells (VECs). Elevation of endothelin levels, due to transcriptional hyperactivation, has been observed in a host of cardiovascular diseases. We have previously shown that serum response factor (SRF) is a regulator of ET1 transcription in VECs. Here we report that angiotensin II (Ang II) induced ET1 transcription paralleled activation of glycogen synthase kinase 3 (GSK3) in cultured VECs. GSK3 knockdown or pharmaceutical inhibition attenuated Ang II induced endothelin expression. Of interest, the effect of GSK3 on endothelin transcription relied on the conserved SRF motif within the ET1 promoter. Further analysis revealed that GSK3 interacted with and phosphorylated SRF at serine 224. Phosphorylation of SRF by GSK3 did not influence its recruitment to the ET1 promoter. Instead, GSK3-mediated SRF phosphorylation potentiated its interaction with MRTF-A, a key co-factor for SRF, which helped recruit the chromatin remodeling protein BRG1 to the ET1 promoter resulting in augmented histone H3 acetylation/H3K4 trimethylation. Consistently, over-expression of a constitutively active GSK enhanced Ang II-induced ET1 transcription and knockdown of either MRTF-A or BRG1 abrogated the enhancement of ET1 transcription. In conclusion, our data highlight a previously unrecognized mechanism that contributes to the transcriptional regulation of endothelin. Targeting this GSK3-SRF axis may yield novel approaches in the intervention of cardiovascular diseases.

A myocardin-adjacent lncRNA balances SRF-dependent gene transcription in the heart

In this study, Anderson et al. identify a cardiac lncRNA transcribed adjacent to myocardin, named CARDINAL, that antagonizes SRF-dependent mitogenic gene transcription in the heart. They also show that CARDINAL forms a nuclear complex with SRF and inhibits TCF-mediated transactivation of the promitogenic gene c-fos, suggesting CARDINAL functions as an essential RNA cofactor for SRF in the heart.

Myocardin, a potent coactivator of serum response factor (SRF), competes with ternary complex factor (TCF) proteins for SRF binding to balance opposing mitogenic and myogenic gene programs in cardiac and smooth muscle. Here we identify a cardiac lncRNA transcribed adjacent to myocardin, named CARDINAL, which antagonizes SRF-dependent mitogenic gene transcription in the heart. CARDINAL-deficient mice show ectopic TCF/SRF-dependent mitogenic gene expression and decreased cardiac contractility in response to age and ischemic stress. CARDINAL forms a nuclear complex with SRF and inhibits TCF-mediated transactivation of the promitogenic gene c-fos, suggesting CARDINAL functions as an RNA cofactor for SRF in the heart.

Optogenetic Control of Myocardin-Related Transcription Factor A Subcellular Localization and Transcriptional Activity Steers Membrane Blebbing and Invasive Cancer Cell Motility

The myocardin-related transcription factor A (MRTF-A) controls the transcriptional activity of the serum response factor (SRF) in a tightly controlled actin-dependent manner. In turn, MRTF-A is crucial for many actin-dependent processes including adhesion, migration, and contractility and has emerged as a novel target for anti-tumor strategies. MRTF-A rapidly shuttles between cytoplasmic and nuclear compartment via dynamic actin interactions within its N-terminal RPEL domain. Here, optogenetics is used to spatiotemporally control MRTF-A nuclear localization by blue light using the light-oxygen-voltage-sensing domain 2-domain based system LEXY (light-inducible nuclear export system). It is found that light-regulated nuclear export of MRTF-A occurs within 10-20 min. Importantly, MRTF-A-LEXY shuttling is independent of perturbations of actin dynamics. Furthermore, light-regulation of MRTF-A-LEXY is reversible and repeatable for several cycles of illumination and its subcellular localization correlates with SRF transcriptional activity. As a consequence, optogenetic control of MRTF-A subcellular localization determines subsequent cytoskeletal dynamics such as non-apoptotic plasma membrane blebbing as well as invasive tumor-cell migration through 3D collagen matrix. This data demonstrates robust optogenetic regulation of MRTF as a powerful tool to control SRF-dependent transcription as well as cell motile behavior.

The distinct roles of myosin IIA and IIB under compression stress in nucleus pulposus cells

Objectives

Inappropriate or excessive compression applied to intervertebral disc (IVD) contributes substantially to IVD degeneration. The actomyosin system plays a leading role in responding to mechanical stimuli. In the present study, we investigated the roles of myosin II isoforms in the compression stress‐induced senescence of nucleus pulposus (NP) cells.

Material and methods

Nucleus pulposus cells were exposed to 1.0 MPa compression for 0, 12, 24 or 36 hours. Immunofluorescence and co‐immunoprecipitation analysis were used to measure the interaction of myosin IIA and IIB with actin. Western blot analysis and immunofluorescence staining were used to detect nuclear expression and nuclear localization of MRTF‐A. In addition, the expression levels of p‐RhoA/RhoA, ROCK1/2 and p‐MLC/MLC were measured in human NP cells under compression stress and in degenerative IVD tissues.

Results

Compression stress increased the interaction of myosin IIA and actin, while the interaction of myosin IIB and actin was reduced. The actomyosin cytoskeleton remodelling was involved in the compression stress‐induced fibrotic phenotype mediated by MRTF‐A nuclear translocation and inhibition of proliferation in NP cells. Furthermore, RhoA/ROCK1 pathway activation mediated compression stress‐induced human NP cells senescence by regulating the interaction of myosin IIA and IIB with actin.

Conclusions

We for the first time investigated the regulation of actomyosin cytoskeleton in human NP cells under compression stress. It provided new insights into the development of therapy for effectively inhibiting IVD degeneration.

Serum response factor, a novel early diagnostic biomarker of acute kidney injury

Objective: Studies have shown that serum response factor (SRF) is increased in chronic kidney injury, such as diabetic nephropathy, hyperuricemic nephropathy and renal cell carcinoma. The objective is to explore the early diagnostic value of SRF in acute kidney injury (AKI).

Methods: AKI-related microarray data were analyzed, and the expression and location of SRF were investigated in the early phase of AKI.

Results: Bioinformatics results demonstrated that SRF was dramatically elevated 2-4 h after ischemia/reperfusion (I/R) in mouse renal tissue. In I/R rats, SRF was mostly expressed and located in renal tubular epithelial cells (TECs). SRF started to increase at 1 h, peaked at 3-9 h and started to decrease at 12 h after I/R. The areas under the ROC curve of renal SRF mRNA, renal SRF protein, urinary SRF, serum SRF and serum creatinine (Scr) were 87.9%, 83.0%, 81.3%, 78.8%, 68.8%, respectively.

Conclusion: SRF is remarkably upregulated in early (before 24 h) AKI and can replace Scr as a potential new early diagnostic biomarker of AKI.

FHOD formin and SRF promote post-embryonic striated muscle growth through separate pathways in C. elegans

Previous work with cultured cells has shown transcription of muscle genes by serum response factor (SRF) can be stimulated by actin polymerization driven by proteins of the formin family. However, it is not clear if endogenous formins similarly promote SRF-dependent transcription during muscle development in vivo. We tested whether formin activity promotes SRF-dependent transcription in striated muscle in the simple animal model, Caenorhabditis elegans. Our lab has shown FHOD-1 is the only formin that directly promotes sarcomere formation in the worm's striated muscle. We show here FHOD-1 and SRF homolog UNC-120 both support muscle growth and also muscle myosin II heavy chain A expression. However, while a hypomorphic unc-120 allele blunts expression of a set of striated muscle genes, these genes are largely upregulated or unchanged by absence of FHOD-1. Instead, pharmacological inhibition of the proteasome restores myosin protein levels in worms lacking FHOD-1, suggesting elevated proteolysis accounts for their myosin deficit. Interestingly, proteasome inhibition does not restore normal muscle growth to fhod-1(Δ) mutants, suggesting formin contributes to muscle growth by some alternative mechanism. Overall, we find SRF does not depend on formin to promote muscle gene transcription in a simple in vivo system.

YY1 directly interacts with myocardin to repress the triad myocardin/SRF/CArG box-mediated smooth muscle gene transcription during smooth muscle phenotypic modulation

Yin Yang 1 (YY1) regulates gene transcription in a variety of biological processes. In this study, we aim to determine the role of YY1 in vascular smooth muscle cell (VSMC) phenotypic modulation both in vivo and in vitro. Here we show that vascular injury in rodent carotid arteries induces YY1 expression along with reduced expression of smooth muscle differentiation markers in the carotids. Consistent with this finding, YY1 expression is induced in differentiated VSMCs in response to serum stimulation. To determine the underlying molecular mechanisms, we found that YY1 suppresses the transcription of CArG box-dependent SMC-specific genes including SM22α, SMα-actin and SMMHC. Interestingly, YY1 suppresses the transcriptional activity of the SM22α promoter by hindering the binding of serum response factor (SRF) to the proximal CArG box. YY1 also suppresses the transcription and the transactivation of myocardin (MYOCD), a master regulator for SMC-specific gene transcription by binding to SRF to form the MYOCD/SRF/CArG box triad (known as the ternary complex). Mechanistically, YY1 directly interacts with MYOCD to competitively displace MYOCD from SRF. This is the first evidence showing that YY1 inhibits SMC differentiation by directly targeting MYOCD. These findings provide new mechanistic insights into the regulatory mechanisms that govern SMC phenotypic modulation in the pathogenesis of vascular diseases.

Signalosome-Regulated Serum Response Factor Phosphorylation Determining Myocyte Growth in Width Versus Length as a Therapeutic Target for Heart Failure

BACKGROUND

Concentric and eccentric cardiac hypertrophy are associated with pressure and volume overload, respectively, in cardiovascular disease both conferring an increased risk of heart failure. These contrasting forms of hypertrophy are characterized by asymmetrical growth of the cardiac myocyte in mainly width or length, respectively. The molecular mechanisms determining myocyte preferential growth in width versus length remain poorly understood. Identification of the mechanisms governing asymmetrical myocyte growth could provide new therapeutic targets for the prevention or treatment of heart failure.

METHODS

Primary adult rat ventricular myocytes, adeno-associated virus (AAV)-mediated gene delivery in mice, and human tissue samples were used to define a regulatory pathway controlling pathological myocyte hypertrophy. Chromatin immunoprecipitation assays with sequencing and precision nuclear run-on sequencing were used to define a transcriptional mechanism.

RESULTS

We report that asymmetrical cardiac myocyte hypertrophy is modulated by SRF (serum response factor) phosphorylation, constituting an epigenomic switch balancing the growth in width versus length of adult ventricular myocytes in vitro and in vivo. SRF Ser103 phosphorylation is bidirectionally regulated by RSK3 (p90 ribosomal S6 kinase type 3) and PP2A (protein phosphatase 2A) at signalosomes organized by the scaffold protein mAKAPβ (muscle A-kinase anchoring protein β), such that increased SRF phosphorylation activates AP-1 (activator protein-1)-dependent enhancers that direct myocyte growth in width. AAV are used to express in vivo mAKAPβ-derived RSK3 and PP2A anchoring disruptor peptides that block the association of the enzymes with the mAKAPβ scaffold. Inhibition of RSK3 signaling prevents concentric cardiac remodeling induced by pressure overload, while inhibition of PP2A signaling prevents eccentric cardiac remodeling induced by myocardial infarction, in each case improving cardiac function. SRF Ser103 phosphorylation is significantly decreased in dilated human hearts, supporting the notion that modulation of the mAKAPβ-SRF signalosome could be a new therapeutic approach for human heart failure.

CONCLUSIONS

We have identified a new molecular switch, namely mAKAPβ signalosome-regulated SRF phosphorylation, that controls a transcriptional program responsible for modulating changes in cardiac myocyte morphology that occur secondary to pathological stressors. Complementary AAV-based gene therapies constitute rationally-designed strategies for a new translational modality for heart failure.

Therapeutic effects of histone deacetylase inhibitors on heart disease

A wide range of histone deacetylase (HDAC) inhibitors have been studied for their therapeutic potential because the excessive activity and expression of HDACs have been implicated in the pathogenesis of cardiac diseases. An increasing number of preclinical studies have demonstrated the cardioprotective effects of numerous HDAC inhibitors, suggesting a wide variety of mechanisms by which the inhibitors protect against cardiac stress, such as the suppression of cardiac fibrosis and fetal gene expression, enhancement of angiogenesis and mitochondrial biogenesis, prevention of electrical remodeling, and regulation of apoptosis, autophagy, and cell cycle arrest. For the development of isoform-selective HDAC inhibitors with high efficacy and low toxicity, it is important to identify and understand the mechanisms responsible for the effects of the inhibitors. This review highlights the preclinical effects of HDAC inhibitors that act against Zn²⁺-dependent HDACs and the underlying mechanisms of their protective effects against cardiac hypertrophy, hypertension, myocardial infarction, heart failure, and atrial fibrillation.

Genetic variant of SRF-rearranged myofibroma with a misleading nuclear expression of STAT6 and STAT6 involvement as 3' fusion partner

Pediatric neoplasms with a myofibroblastic differentiation are frequent in children, in particular myofibroma. Recently, a novel deep soft tissue myofibroblastic neoplasm has been described with high cellularity, a smooth muscle phenotype and SRF-RELA fusion. We report the case of a 15-year-old boy who presented with a tumor of the deep soft tissue of the arm, with overlapping histological features with the recently described SRF-RELA group of myofibromas but differing by the presence of calcifications, a novel SRF-STAT6 fusion transcript and nuclear expression of STAT6. No local recurrence nor distant metastasis was detected at the current follow-up of 29 months. The clinical relevance of this novel fusion requires further investigations.

Changes in snail and SRF expression in the kidneys of diabetic rats during ageing

BACKGROUND

Diabetic nephropathy is a progressive condition which develops for many years. We analyzed expression of Snail and serum response factor (SRF), epithelial-mesenchymal transition (EMT) regulatory transcription factors with a key role in renal fibrosis, in different renal areas of diabetic rats during ageing.

METHODS

Male Sprague-Dawley rats were treated with 55 mg/kg streptozotocin (model of type 1 diabetes mellitus; DM group) or citrate buffer (control). DM group received insulin weekly to prevent ketoacidosis. After 2 weeks, 2, 6 and 12 months kidney samples were collected and analysed in different renal areas.

RESULTS

Snail expression was located within cortex in proximal convoluted tubules, in control and DM groups, in the cytoplasm. Percentage of Snail-positive cells in control groups was high and decreased with time, whereas in DM groups the highest percentage was after 2 weeks. In all time points, smaller percentage of Snail expression was seen in DM groups compared to controls. SRF expression was mostly located in the proximal convoluted tubules, always in the cytoplasm. In control groups SRF was expressed in all time periods in proximal convoluted tubules, with decrement after 12 months. Percentage of SRF-positive cells was higher in control groups compared to DM in all time points, with the exception of 12 months. To a smaller degree, SRF expression was seen in the glomeruli and distal convoluted tubules, with more SRF positive cells in DM compared to their control groups.

CONCLUSIONS

While Snail expression remained lower in diabetic tissues, compared to controls, expression of SRF increased in diabetic tissues in the second part of the year. These changes may need long time to develop, and, in line with earlier reports, it is possible that insulin treatment of DM rats once a week reduces possibility of EMT and development of renal fibrosis even in the long term.

Transcription Factors Targeted by miRNAs Regulating Smooth Muscle Cell Growth and Intimal Thickening after Vascular Injury

Neointima formation after percutaneous coronary intervention (PCI) is a manifestation of “phenotype switching” by vascular smooth muscle cells (SMC), a process that involves de-differentiation from a contractile quiescent phenotype to one that is richly synthetic. In response to injury, SMCs migrate, proliferate, down-regulate SMC-specific differentiation genes, and later, can revert to the contractile phenotype. The vascular response to injury is regulated by microRNAs (or miRNAs), small non-coding RNAs that control gene expression. Interactions between miRNAs and transcription factors impact gene regulatory networks. This article briefly reviews the roles of a range of miRNAs in molecular and cellular processes that control intimal thickening, focusing mainly on transcription factors, some of which are encoded by immediate-early genes. Examples include Egr-1, junB, KLF4, KLF5, Elk-1, Ets-1, HMGB1, Smad1, Smad3, FoxO4, SRF, Rb, Sp1 and c-Myb. Such mechanistic information could inform the development of strategies that block SMC growth, neointima formation, and potentially overcome limitations of lasting efficacy following PCI.

Protein Kinase N Promotes Stress-Induced Cardiac Dysfunction Through Phosphorylation of Myocardin-Related Transcription Factor A and Disruption of Its Interaction With Actin

BACKGROUND

Heart failure is a complex syndrome that results from structural or functional impairment of ventricular filling or blood ejection. Protein phosphorylation is a major and essential intracellular mechanism that mediates various cellular processes in cardiomyocytes in response to extracellular and intracellular signals. The RHOA-associated protein kinase (ROCK/Rho-kinase), an effector regulated by the small GTPase RHOA, causes pathological phosphorylation of proteins, resulting in cardiovascular diseases. RHOA also activates protein kinase N (PKN); however, the role of PKN in cardiovascular diseases remains unclear.

METHODS

To explore the role of PKNs in heart failure, we generated tamoxifen-inducible, cardiomyocyte-specific PKN1- and PKN2-knockout mice by intercrossing the αMHC-CreERT2 line with Pkn1^flox/flox and Pkn2^flox/flox mice and applied a mouse model of transverse aortic constriction- and angiotensin II-induced heart failure. To identify a novel substrate of PKNs, we incubated GST-tagged myocardin-related transcription factor A (MRTFA) with recombinant GST-PKN-catalytic domain or GST-ROCK-catalytic domain in the presence of radiolabeled ATP and detected radioactive GST-MRTFA as phosphorylated MRTFA.

RESULTS

We demonstrated that RHOA activates 2 members of the PKN family of proteins, PKN1 and PKN2, in cardiomyocytes of mice with cardiac dysfunction. Cardiomyocyte-specific deletion of the genes encoding Pkn1 and Pkn2 (cmc-PKN1/2 DKO) did not affect basal heart function but protected mice from pressure overload- and angiotensin II-induced cardiac dysfunction. Furthermore, we identified MRTFA as a novel substrate of PKN1 and PKN2 and found that MRTFA phosphorylation by PKN was considerably more effective than that by ROCK in vitro. We confirmed that endogenous MRTFA phosphorylation in the heart was induced by pressure overload- and angiotensin II-induced cardiac dysfunction in wild-type mice, whereas cmc-PKN1/2 DKO mice suppressed transverse aortic constriction- and angiotensin II-induced phosphorylation of MRTFA. Although RHOA-mediated actin polymerization accelerated MRTFA-induced gene transcription, PKN1 and PKN2 inhibited the interaction of MRTFA with globular actin by phosphorylating MRTFA, causing increased serum response factor-mediated expression of cardiac hypertrophy- and fibrosis-associated genes.

CONCLUSIONS

Our results indicate that PKN1 and PKN2 activation causes cardiac dysfunction and is involved in the transition to heart failure, thus providing unique targets for therapeutic intervention for heart failure.

MRTFA augments megakaryocyte maturation by enhancing the SRF regulatory axis

Serum response factor (SRF) is a ubiquitously expressed transcription factor that binds DNA at CArG (CC[A/T]₆GG) domains in association with myocardin-family proteins (eg, myocardin-related transcription factor A [MRTFA]) or the ternary complex factor family of E26 transformation-specific (ETS) proteins. In primary hematopoietic cells, knockout of either SRF or MRTFA decreases megakaryocyte (Mk) maturation causing thrombocytopenia. The human erythroleukemia (HEL) cell line mimics the effects of MRTFA on Mk maturation, and MRTFA overexpression (MRTFA^OE) in HEL cells enhances megakaryopoiesis. To identify the mechanisms underlying these effects, we performed integrated analyses of anti-SRF chromatin immunoprecipitation (ChIP) and RNA-sequencing data from noninduced and phorbol ester (12-O-tetradecanoylphorbol-13-acetate [TPA])-induced HEL cells, with and without MRTFA^OE We found that 11% of genes were upregulated with TPA induction, which was enhanced by MRTFA^OE, resulting in an upregulation of 25% of genes. MRTFA^OE increased binding of SRF to genomic sites and enhanced TPA-induced expression of SRF target genes. The TPA-induced genes are predicted to be regulated by SRF and ETS factors, whereas those upregulated by TPA plus MRTFA^OE lack ETS binding motifs, and MRTFA^OE skews SRF binding to genomic regions with CArG sites in regions relatively lacking in ETS binding motifs. Finally, ChIP-polymerase chain reaction using HEL cells and primary human CD34⁺ cell-derived subpopulations confirms that both SRF and MRTFA have increased binding during megakaryopoiesis at upregulated target genes (eg, CORO1A). We show for the first time that MRTFA increases both the genomic association and activity of SRF and upregulates genes that enhance primary human megakaryopoiesis.