Spatial coordination of actin polymerization and ILK-Akt2 activity during endothelial cell migration

Thymosin β4 promotes zebrafish Mauthner axon regeneration by facilitating actin polymerization through binding to G-actin

BACKGROUND

Thymosin beta 4 (Tβ4) is a monomeric actin-binding protein that plays many roles in biological activities. However, some studies on the role of Tβ4 in central axon regeneration have yielded contradictory results. Previous research has focused primarily on cultured cells, leading to a deficiency in in vivo experimental evidence. Therefore, we used a single axon injury model of Mauthner cells in zebrafish larvae to investigate the role of Tβ4 in central axon regeneration in vivo.

RESULTS

Our results demonstrated that knockout of Tβ4 impaired axon regeneration, whereas overexpression of Tβ4 promoted axon regeneration. Moreover, this promotion is mediated through the interaction between Tβ4 and G-actin. Furthermore, our results suggest that the binding of Tβ4 to G-actin promotes actin polymerization rather than depolymerization. In the rapid escape behavior test, larvae with damaged axons presented impaired tail muscle control, resulting in a lack of normal tail bending, termed the straight tail phenomenon. The proportion of straight tails was significantly negatively correlated with axon regeneration length, suggesting that it is a new indicator for assessing rapid escape behavior recovery. Finally, the results showed that the overexpression of Tβ4 effectively restored the functionality of rapid escape behaviors mediated by Mauthner cells.

CONCLUSIONS

Our results provide evidence that Tβ4 promotes central axon regeneration in vivo through binding to G-actin and suggest that Tβ4 could serve as a potential polypeptide drug for clinical therapy.

CD99 Modulates the Proteomic Landscape of Ewing Sarcoma Cells and Related Extracellular Vesicles

Ewing sarcoma (EWS) is an aggressive pediatric bone tumor characterized by unmet clinical needs and an incompletely understood epigenetic heterogeneity. Here, we considered CD99, a major surface molecule hallmark of EWS malignancy. Fluctuations in CD99 expression strongly impair cell dissemination, differentiation, and death. CD99 is also loaded within extracellular vesicles (EVs), and the delivery of CD99-positive or CD99-negative EVs dynamically exerts oncogenic or oncosuppressive functions to recipient cells, respectively. We undertook mass spectrometry and functional annotation analysis to investigate the consequences of CD99 silencing on the proteomic landscape of EWS cells and related EVs. Our data demonstrate that (i) the decrease in CD99 leads to major changes in the proteomic profile of EWS cells and EVs; (ii) intracellular and extracellular compartments display two distinct signatures of differentially expressed proteins; (iii) proteomic changes converge to the modulation of cell migration and immune-modulation biological processes; and (iv) CD99-silenced cells and related EVs are characterized by a migration-suppressive, pro-immunostimulatory proteomic profile. Overall, our data provide a novel source of CD99-associated protein biomarkers to be considered for further validation as mediators of EWS malignancy and as EWS disease liquid biopsy markers.

The Pathophysiological Role of Thymosin β4 in the Kidney Glomerulus

Diseases affecting the glomerulus, the filtration unit of the kidney, are a major cause of chronic kidney disease. Glomerular disease is characterised by injury of glomerular cells and is often accompanied by an inflammatory response that drives disease progression. New strategies are needed to slow the progression to end-stage kidney disease, which requires dialysis or transplantation. Thymosin β4 (Tβ4), an endogenous peptide that sequesters G-actin, has shown potent anti-inflammatory function in experimental models of heart, kidney, liver, lung, and eye injury. In this review, we discuss the role of endogenous and exogenous Tβ4 in glomerular disease progression and the current understanding of the underlying mechanisms.

New Perspectives on the Role of Integrin-Linked Kinase (ILK) Signaling in Cancer Metastasis

Simple Summary

Today, the vast majority of deaths from cancer are due to cancer metastasis. Metastasis requires that cancer cells escape from the initial tumor, travel through blood vessels, and form new tumors in distant host tissues. Integrin-linked kinase (ILK) is overexpressed by many types of cancer cells and provides both structural and signaling functions that are important for successful metastasis. Here, we discuss recent findings that show how ILK is involved in promoting physical changes important for cell motility and invasion, and how ILK relays signals to other machinery components during metastasis, including interactions with components of the immune system and communication between cancer cells and normal cells, to affect the process of metastasis. We also discuss the contribution of ILK to therapeutic resistance and examine efforts to target ILK for the treatment of metastatic disease.

Abstract

Cancer metastasis is a major barrier to the long-term survival of cancer patients. In cancer cells, integrin engagement downstream of cell-extracellular matrix (ECM) interactions results in the recruitment of cytoskeletal and signaling molecules to form multi-protein complexes to promote processes critical for metastasis. One of the major functional components of these complexes is Integrin Linked Kinase (ILK). Here, we discuss recent advances in our understanding of the importance of ILK as a signaling effector in processes linked to tumor progression and metastasis. New mechanistic insights as to the role of ILK in cellular plasticity, epithelial mesenchymal transition (EMT), migration, and invasion, including the impact of ILK on the formation of invadopodia, filopodia-like protrusions (FLPs), and Neutrophil Extracellular Trap (NET)-induced motility are highlighted. Recent findings detailing the contribution of ILK to therapeutic resistance and the importance of ILK as a potentially therapeutically tractable vulnerability in both solid tumors and hematologic malignancies are discussed. Indeed, pharmacologic inhibition of ILK activity using specific small molecule inhibitors is effective in curtailing the contribution of ILK to these processes, potentially offering a novel therapeutic avenue for inhibiting critical steps in the metastatic cascade leading to reduced drug resistance and increased therapeutic efficacy.

Oxidative Stress Modulation by Carnosine in Scaffold Free Human Dermis Spheroids Model: A Proteomic Study

Carnosine is an endogenous β-alanyl-L-histidine dipeptide endowed with antioxidant and carbonyl scavenger properties, which is able to significantly prevent the visible signs of aging and photoaging. To investigate the mechanism of action of carnosine on human skin proteome, a 3D scaffold-free spheroid model of primary dermal fibroblasts from a 50-year-old donor was adopted in combination with quantitative proteomics for the first time. The label free proteomics approach based on high-resolution mass spectrometry, integrated with network analyses, provided a highly sensitive and selective method to describe the human dermis spheroid model during long-term culture and upon carnosine treatment. Overall, 2171 quantified proteins allowed the in-depth characterization of the 3D dermis phenotype during growth and differentiation, at 14 versus 7 days of culture. A total of 485 proteins were differentially regulated by carnosine at 7 days, an intermediate time of culture. Of the several modulated pathways, most are involved in mitochondrial functionality, such as oxidative phosphorylation, TCA cycle, extracellular matrix reorganization and apoptosis. In long-term culture, functional modules related to oxidative stress were upregulated, inducing the aging process of dermis spheroids, while carnosine treatment prevented this by the downregulation of the same functional modules. The application of quantitative proteomics, coupled to advanced and relevant in vitro scaffold free spheroids, represents a new concrete application for personalized therapies and a novel care approach.

Extra-Nuclear Functions of the Transcription Factor Grainyhead-Like 3 in the Endothelium-Interaction with Endothelial Nitric Oxide Synthase

We previously demonstrated that the transcription factor Grainyhead-like 3 (GRHL3) has essential functions in endothelial cells by inhibiting apoptosis and promoting migration as well as activation of endothelial nitric oxide synthase (eNOS). We now show that a large portion of the protein is localized to myo-endothelial projections of murine arteries suggesting extra-nuclear functions. Therefore, we generated various deletion mutants to identify the nuclear localization signal (NLS) of GRHL3 and assessed potential extra-nuclear functions. Several large-scale deletion mutants were incapable of activating a GRHL3-dependent reporter construct, which could either be due to deficiencies in transcriptional activation or to impaired nuclear import. One of these mutants encompassed a predicted bipartite NLS whose deletion led to the retention of GRHL3 outside the nucleus. Interestingly, this mutant retained functions of the full-length protein as it could still inhibit pathways inducing endothelial cell apoptosis. As apoptosis protection by GRHL3 depends on NO-production, we examined whether GRHL3 could interact with eNOS and showed a direct interaction, which was enhanced with the extra-nuclear GRHL3 variant. The observation that endogenous GRHL3 also interacts with eNOS in intact murine arteries corroborated these findings and substantiated the notion that GRHL3 has important extra-nuclear functions in the endothelium.

The developmental competence of bovine oocytes matured in vitro using thymosin beta 4

The aim of this study was to examine the effect of thymosin beta 4 (Tβ4) during in vitro maturation (IVM) of oocytes and subsequent embryonic development after in vitro fertilization as well as to assess the quality of obtained blastocysts. Cumulus-oocyte complexes (COCs) were matured in vitro in 4 different media: 1. control medium; 2. control media supplemented with 50 ng/mL Tβ4; 3. control media supplemented with 0.5 mg/mL Tβ4; and 4. control media supplemented with 1 mg/mL Tβ4. The quality of the developed blastocysts was analysed by the TUNEL method. The number of cleaved eggs was significantly higher (P<0.05) when gametes were matured in the presence of 50 ng/mL Tβ4 than it was using the other types of media. Additionally, the largest number of blastocysts was observed when 0.5 mg Tβ4 was added to the medium (P<0.05). No significant difference was noted in the mean number of apoptotic nuclei per blastocyst or in the mean number of nuclei per blastocyst in any of the analysed groups. In conclusion, Tβ4 supplementation (50 ng/mL) in maturation medium increased the number of cleaved oocytes, and the number of blastocysts obtained increased when 0.5 mg/mL Tβ4 was used. This positive effect was not observed when a higher concentration of Tβ4 (1 mg/mL) was used.

Progress on the Function and Application of Thymosin β4

Thymosin β4 (Tβ4) is a multifunctional and widely distributed peptide that plays a pivotal role in several physiological and pathological processes in the body, namely, increasing angiogenesis and proliferation and inhibiting apoptosis and inflammation. Moreover, Tβ4 is effectively utilized for several indications in animal experiments or clinical trials, such as myocardial infarction and myocardial ischemia-reperfusion injury, xerophthalmia, liver and renal fibrosis, ulcerative colitis and colon cancer, and skin trauma. Recent studies have reported the potential application of Tβ4 and its underlying mechanisms. The present study reveals the progress regarding functions and applications of Tβ4.

Thymosin β4 is essential for adherens junction stability and epidermal planar cell polarity

Planar cell polarity (PCP) is essential for tissue morphogenesis and homeostasis; however, the mechanisms that orchestrate the cell shape and packing dynamics required to establish PCP are poorly understood. Here, we identified a major role for the globular (G)-actin-binding protein thymosin-β4 (TMSB4X) in PCP establishment and cell adhesion in the developing epidermis. Depletion of Tmsb4x in mouse embryos hindered eyelid closure and hair-follicle angling owing to PCP defects. Tmsb4x depletion did not preclude epidermal cell adhesion in vivo or in vitro; however, it resulted in abnormal structural organization and stability of adherens junction (AJ) due to defects in filamentous (F)-actin and G-actin distribution. In cultured keratinocytes, TMSB4X depletion increased the perijunctional G/F-actin ratio and decreased G-actin incorporation into junctional actin networks, but it did not change the overall actin expression level or cellular F-actin content. A pharmacological treatment that increased the G/F-actin ratio and decreased actin polymerization mimicked the effects of Tmsb4x depletion on both AJs and PCP. Our results provide insights into the regulation of the actin pool and its involvement in AJ function and PCP establishment.

Highlighted Article: By regulating actin pool distribution and incorporation into junctional actin networks, thymosin β4 regulates cell–cell adhesion, planar cell polarity and epidermal morphogenesis.

A dimeric thymosin beta 4 with novel bio-activity protects post-ischemic cardiac function by accelerating vascular endothelial cell proliferation

BACKGROUND

Thymosin beta 4 (Tβ4) is a 43-amino-acid peptide with protective properties in myocardium injury. Previously, we produced a recombinant human dimeric Tβ4 (DTβ4). Here, the cardioprotective effects of DTβ4 and the molecular mechanisms underlying its enhanced activity were investigated.

METHODS AND RESULTS

Echocardiography measurements showed that the cardioprotective effect of DTβ4 in myocardial infarction mice was significantly higher than that of wild-type Tβ4. Corresponding in vitro analyses demonstrated that the enhanced cardioprotection provided by DTβ4 was largely due to increased stimulation of angiogenesis. HPLC analysis, western blotting and qRT-PCR indicated that the enhanced pro-angiogenesis activity of DTβ4 was independent of the protein half-life and the known downstream pathways of wild-type Tβ4. Transcriptome deep sequencing (RNA-seq), BrdU incorporation assays, flow cytometry analysis and RNA interference demonstrated that the enhanced angiogenic activity of DTβ4 depended on MALAT1 (metastasis-associated lung adenocarcinoma transcript 1)-induced proliferation of vascular endothelial cells, which has not been reported for wild-type Tβ4. Moreover, transcription factor activation screening, luciferase promoter reporter assay and immunoprecipitation assay demonstrated that DTβ4 enhanced MALAT1 transcription by inhibiting the degradation of prospero-related homeobox 1 (PROX1).

CONCLUSION

This study demonstrates the potential applications and the novel bioactivity of the Tβ4 dimer. Moreover, to construct the dimer represents a new method for production of bioactive peptides that may have novel activities.

Reconsidering an active role for G-actin in cytoskeletal regulation

Globular (G)-actin, the actin monomer, assembles into polarized filaments that form networks that can provide structural support, generate force and organize the cell. Many of these structures are highly dynamic and to maintain them, the cell relies on a large reserve of monomers. Classically, the G-actin pool has been thought of as homogenous. However, recent work has shown that actin monomers can exist in distinct groups that can be targeted to specific networks, where they drive and modify filament assembly in ways that can have profound effects on cellular behavior. This Review focuses on the potential factors that could create functionally distinct pools of actin monomers in the cell, including differences between the actin isoforms and the regulation of G-actin by monomer binding proteins, such as profilin and thymosin β4. Owing to difficulties in studying and visualizing G-actin, our knowledge over the precise role that specific actin monomer pools play in regulating cellular actin dynamics remains incomplete. Here, we discuss some of these unanswered questions and also provide a summary of the methodologies currently available for the imaging of G-actin.

Molecular signatures of differential responses to exercise trainings during rehabilitation

The loss and recovery of muscle mass and function following injury and during rehabilitation varies among individuals. While recent expression profiling studies have illustrated transcriptomic responses to muscle disuse and remodeling, how these changes contribute to the physiological responses are not clear. In this study, we quantified the effects of immobilization and subsequent rehabilitation training on muscle size and identified molecular pathways associated with muscle responsiveness in an orthopaedic patient cohort study. The injured leg of 16 individuals with ankle injury was immobilized for a minimum of 4 weeks, followed by a 6-week rehabilitation program. The maximal cross-sectional area (CSA) of the medial gastrocnemius muscle of the immobilized and control legs were determined by T1-weighted axial MRI images. Genome-wide mRNA profiling data were used to identify molecular signatures that distinguish the patients who responded to immobilization and rehabilitation and those who were considered minimal responders. RESULTS: Using 6% change as the threshold to define responsiveness, a greater degree of changes in muscle size was noted in high responders (−14.9 ± 3.6%) compared to low responders (0.1 ± 0.0%) during immobilization. In addition, a greater degree of changes in muscle size was observed in high responders (20.5 ± 3.2%) compared to low responders (2.5 ± 0.9%) at 6-week rehabilitation. Microarray analysis showed a higher number of genes differentially expressed in the responders compared to low responders in general; with more expression changes observed at the acute stage of rehabilitation in both groups. Pathways analysis revealed top molecular pathways differentially affected in the groups, including genes involved in mitochondrial function, protein turn over, integrin signaling and inflammation. This study confirmed the extent of muscle atrophy due to immobilization and recovery by exercise training is associated with distinct remodeling signature, which can potentially be used for evaluating and predicting clinical outcomes.

Tumor microenvironment conditions alter Akt and Na+/H+ exchanger NHE1 expression in endothelial cells more than hypoxia alone: implications for endothelial cell function in cancer

BACKGROUND

Chronic angiogenesis is a hallmark of most tumors and takes place in a hostile tumor microenvironment (TME) characterized by hypoxia, low nutrient and glucose levels, elevated lactate and low pH. Despite this, most studies addressing angiogenic signaling use hypoxia as a proxy for tumor conditions. Here, we compared the effects of hypoxia and TME conditions on regulation of the Na⁺/H⁺ exchanger NHE1, Ser/Thr kinases Akt1-3, and downstream effectors in endothelial cells.

METHODS

Human umbilical vein endothelial cells (HUVEC) and Ea.hy926 endothelial cells were exposed to simulated TME (1% hypoxia, low serum, glucose, pH, high lactate) or 1% hypoxia for 24 or 48 h, with or without NHE1 inhibition or siRNA-mediated knockdown. mRNA and protein levels of NHE1, Akt1-3, and downstream effectors were assessed by qPCR and Western blotting, vascular endothelial growth factor (VEGF) release by ELISA, and motility by scratch assay.

RESULTS

Within 24 h, HIF-1α level and VEGF mRNA level were increased robustly by TME and modestly by hypoxia alone. The NHE1 mRNA level was decreased by both hypoxia and TME, and NHE1 protein was reduced by TME in Ea.hy926 cells. Akt1-3 mRNA was detected in HUVEC and Ea.hy926 cells, Akt1 most abundantly. Akt1 protein expression was reduced by TME yet unaffected by hypoxia, while Akt phosphorylation was increased by TME. The Akt loss was partly reversed by MCF-7 human breast cancer cell conditioned medium, suggesting that in vivo, the cancer cell secretome may compensate for adverse effects of TME on endothelial cells. TME, yet not hypoxia, reduced p70S6 kinase activity and ribosomal protein S6 phosphorylation and increased eIF2α phosphorylation, consistent with inhibition of protein translation. Finally, TME reduced Retinoblastoma protein phosphorylation and induced poly-ADP-ribose polymerase (PARP) cleavage consistent with inhibition of proliferation and induction of apoptosis. NHE1 knockdown, mimicking the effect of TME on NHE1 expression, reduced Ea.hy926 migration. TME effects on HIF-1α, VEGF, Akt, translation, proliferation or apoptosis markers were unaffected by NHE1 knockdown/inhibition.

CONCLUSIONS

NHE1 and Akt are downregulated by TME conditions, more potently than by hypoxia alone. This inhibits endothelial cell migration and growth in a manner likely modulated by the cancer cell secretome.

cPLA2α activates PI3K/AKT and inhibits Smad2/3 during epithelial-mesenchymal transition of hepatocellular carcinoma cells

Cytosolic phospholipase A2α (cPLA2α), a key phospholipase that regulates lipid metabolism, plays an important role in tumor progression. In the present study of hepatocellular carcinoma (HCC), cPLA2α was overexpressed in highly metastatic HCC cell lines. Immunohistochemical staining showed increased levels of cPLA2α at the invasive edges of HCC, and a clinicopathological analysis of samples from 111 patients revealed that its expression level was linked with micro-vascular invasion and cirrhosis. Knockdown of cPLA2α inhibited migration, probably due to its role in actin polymerization. Overexpression of cPLA2α promoted cell migration and invasion. Based on the mechanistic analysis, our data suggested that cPLA2α mediate epidermal growth factor (EGF) induced epithelial-mesenchymal transition (EMT) through PI3K/AKT/ERK pathway. cPLA2α activity was required for the transforming growth factor-(TGF)-β-induced EMT. However, cPLA2α inhibited Smad2/3 activation and promoted the activation of the PI3K/AKT/ERK pathway. A xenograft tumor transplant model confirmed the role of cPLA2α in HCC invasion and metastasis. Based on the mechanistic analysis, cPLA2α mediated both EGF- and TGF-β-induced EMT, which are essential for HCC metastasis. cPLA2α is a potentially target for novel therapies of HCC.

Aberrant developmental titin splicing and dysregulated sarcomere length in Thymosin β4 knockout mice

Sarcomere assembly is a highly orchestrated and dynamic process which adapts, during perinatal development, to accommodate growth of the heart. Sarcomeric components, including titin, undergo an isoform transition to adjust ventricular filling. Many sarcomeric genes have been implicated in congenital cardiomyopathies, such that understanding developmental sarcomere transitions will inform the aetiology and treatment. We sought to determine whether Thymosin β4 (Tβ4), a peptide that regulates the availability of actin monomers for polymerization in non-muscle cells, plays a role in sarcomere assembly during cardiac morphogenesis and influences adult cardiac function. In Tβ4 null mice, immunofluorescence-based sarcomere analyses revealed shortened thin filament, sarcomere and titin spring length in cardiomyocytes, associated with precocious up-regulation of the short titin isoforms during the postnatal splicing transition. By magnetic resonance imaging, this manifested as diminished stroke volume and limited contractile reserve in adult mice. Extrapolating to an in vitro cardiomyocyte model, the altered postnatal splicing was corrected with addition of synthetic Tβ4, whereby normal sarcomere length was restored. Our data suggest that Tβ4 is required for setting correct sarcomere length and for appropriate splicing of titin, not only in the heart but also in skeletal muscle. Distinguishing between thin filament extension and titin splicing as the primary defect is challenging, as these events are intimately linked. The regulation of titin splicing is a previously unrecognised role of Tβ4 and gives preliminary insight into a mechanism by which titin isoforms may be manipulated to correct cardiac dysfunction.

Loss of endogenous thymosin β4 accelerates glomerular disease

Glomerular disease is characterized by morphologic changes in podocyte cells accompanied by inflammation and fibrosis. Thymosin β₄ regulates cell morphology, inflammation, and fibrosis in several organs and administration of exogenous thymosin β₄ improves animal models of unilateral ureteral obstruction and diabetic nephropathy. However, the role of endogenous thymosin β₄ in the kidney is unknown. We demonstrate that thymosin β₄ is expressed prominently in podocytes of developing and adult mouse glomeruli. Global loss of thymosin β₄ did not affect healthy glomeruli, but accelerated the severity of immune-mediated nephrotoxic nephritis with worse renal function, periglomerular inflammation, and fibrosis. Lack of thymosin β₄ in nephrotoxic nephritis led to the redistribution of podocytes from the glomerular tuft toward the Bowman capsule suggesting a role for thymosin β₄ in the migration of these cells. Thymosin β₄ knockdown in cultured podocytes also increased migration in a wound-healing assay, accompanied by F-actin rearrangement and increased RhoA activity. We propose that endogenous thymosin β₄ is a modifier of glomerular injury, likely having a protective role acting as a brake to slow disease progression.

Cardioprotection by Thymosin Beta 4

Treatment with thymosin beta 4 (Tβ4) reduces infarct volume and preserves cardiac function in preclinical models of cardiac ischemic injury. These effects stem in part from decreased infarct size, but additional benefits are likely due to specific antifibrotic and proangiogenic activities. Injected or transgenic Tβ4 increase blood vessel growth in large and small animal models, consistent with Tβ4 converting hibernating myocardium to an actively contractile state following ischemia. Tβ4 and its degradation products have antifibrotic effects in in vitro assays and in animal models of fibrosis not related to cardiac injury. This large number of pleiotropic effects results from Tβ4's many interactions with cellular signaling pathways, particularly indirect regulation of cellular motility and movement via the SRF-MRTF-G-actin transcriptional pathway. Variation in effects and effect sizes in animal models may potentially be due to variable distribution of Tβ4. Preclinical studies of PK/PD relationships and a reliable pharmacodynamic biomarker would facilitate clinical development of Tβ4.

Intrinsic, Functional, and Structural Properties of β-Thymosins and β-Thymosin/WH2 Domains in the Regulation and Coordination of Actin Self-Assembly Dynamics and Cytoskeleton Remodeling

β-Thymosins are a family of heat-stable multifunctional polypeptides that are expressed as small proteins of about 5kDa (~45 amino acids) almost exclusively in multicellular animals. They were first isolated from the thymus. As full-length or truncated polypeptides, they appear to stimulate a broad range of extracellular activities in various signaling pathways, including tissue repair and regeneration, inflammation, cell migration, and immune defense. However, their cell surface receptors and structural mechanisms of regulations in these multiple pathways remain still poorly understood. Besides their extracellular activities, they belong to a larger family of small, intrinsically disordered actin-binding domains called WH2/β-thymosin domains that have been identified in more than 1800 multidomain proteins found in different taxonomic domains of life and involved in various actin-based motile processes including cell morphogenesis, motility, adhesions, tissue development, intracellular trafficking, or pathogen infections. This review briefly surveys the main recent findings to understand how these small, intrinsically disordered but functional domains can interact with many unrelated partners and can thus integrate and coordinate various intracellular activities in actin self-assembly dynamics and cell signaling pathways linked to their cytoskeleton remodeling.

Systemic Dosing of Thymosin Beta 4 before and after Ischemia Does Not Attenuate Global Myocardial Ischemia-Reperfusion Injury in Pigs

The use of cardiopulmonary bypass (CPB) and aortic cross-clamping causes myocardial ischemia-reperfusion injury (I-RI) and can lead to reduced postoperative cardiac function. We investigated whether this injury could be attenuated by thymosin beta 4 (TB4), a peptide which has showed cardioprotective effects. Pigs received either TB4 or vehicle and underwent CPB and aortic cross-clamping for 60 min with cold intermittent blood-cardioplegia and were then followed for 30 h. Myocardial function and blood flow was studied by cardiac magnetic resonance and PET imaging. Tissue and plasma samples were analyzed to determine the amount of cardiomyocyte necrosis and apoptosis as well as pharmacokinetics of the peptide. In vitro studies were performed to assess its influence on blood coagulation and vasomotor tone. Serum levels of the peptide were increased after administration compared to control samples. TB4 did not decrease the amount of cell death. Cardiac function and global myocardial blood flow was similar between the study groups. At high doses a vasoconstrictor effect on mesentery arteries and a vasodilator effect on coronary arteries was observed and blood clot firmness was reduced when tested in the presence of an antiplatelet agent. Despite promising results in previous trials the cardioprotective effect of TB4 was not demonstrated in this model for global myocardial I-RI.

Development of the intein-mediated method for production of recombinant thymosin β4 from the acetylated in vivo fusion protein

Thymosin β4 is a 43 amino acid long peptide with an acetylated N-terminal serin that has a high potential as a remedy for healing ulcers, wounds and burns. Although protein biosynthesis offers attractive opportunities in terms of a large-scale production, currently thymosin β4 is mainly produced by chemical synthesis. The problems that hinder the successful commercialization of the biotechnological approach are associated with the small peptides expression and N-terminal acetylation. This work presents an innovative biotechnological method for thymosin β4 production that employs the peptide acetylation in vivo. A genetically engineered construct was created, where the Tβ4 coding sequence fused with the intein Mxe GyrA sequence and chitin-binding domain was combined with the acetyltransferase coding sequence to form a polycistronic construct under a stringent control of T7 promoter. This plasmid construct provided for the expression of the Tβ4-intein fusion protein. In the process of the post-translational modification in vivo formyl methionine was completely removed from the target peptide N-terminus and followed by the Tβ4 precursor N-terminal acetylation. The use of the intein-mediated expression system made it possible to extract thymosin β4 in only 2 chromatographic runs. The method is straightforward to implement and scale up.

Functional specificity of Akt isoforms in cancer progression

Akt/PKB kinases are central mediators of cell homeostasis. There are three highly homologous Akt isoforms, Akt1/PKBα, Akt2/PKBβ and Akt3/PKBγ. Hyperactivation of Akt signaling is a key node in the progression of a variety of human cancer, by modulating tumor growth, chemoresistance and cancer cell migration, invasion and metastasis. It is now clear that, to understand the mechanisms on how Akt affects specific cancer cells, it is necessary to consider the relative importance of each of the three Akt isoforms in the altered cells. Akt1 is involved in tumor growth, cancer cell invasion and chemoresistance and is the predominant altered isoform found in various carcinomas. Akt2 is related to cancer cell invasion, metastasis and survival more than tumor induction. Most of the Akt2 alterations are observed in breast, ovarian, pancreatic and colorectal carcinomas. As Akt3 expression is limited to some tissues, its implication in tumor growth and resistance to drugs mostly occurs in melanomas, gliomas and some breast carcinomas. To explain how Akt isoforms can play different or even opposed roles, three mechanisms have been proposed: tissue-specificity expression/activation of Akt isoforms, distinct effect on same substrate as well as specific localization through the cyto-skeleton network. It is becoming clear that to develop an effective anticancer Akt inhibitor drug, it is necessary to target the specific Akt isoform which promotes the progression of the specific tumor.

Two functionally distinct sources of actin monomers supply the leading edge of lamellipodia

Lamellipodia, the sheet-like protrusions of motile cells, consist of networks of actin filaments (F-actin) regulated by the ordered assembly from and disassembly into actin monomers (G-actin). Traditionally, G-actin is thought to exist as a homogeneous pool. Here, we show that there are two functionally and molecularly distinct sources of G-actin that supply lamellipodial actin networks. G-actin originating from the cytosolic pool requires the monomer-binding protein thymosin β4 (Tβ4) for optimal leading-edge localization, is targeted to formins, and is responsible for creating an elevated G/F-actin ratio that promotes membrane protrusion. The second source of G-actin comes from recycled lamellipodia F-actin. Recycling occurs independently of Tβ4 and appears to regulate lamellipodia homeostasis. Tβ4-bound G-actin specifically localizes to the leading edge because it does not interact with Arp2/3-mediated polymerization sites found throughout the lamellipodia. These findings demonstrate that actin networks can be constructed from multiple sources of monomers with discrete spatiotemporal functions.

Two functionally distinct sources of actin monomers supply the leading edge of lamellipodia

Lamellipodia, the sheet-like protrusions of motile cells, consist of networks of actin filaments (F-actin) regulated by the ordered assembly from and disassembly into actin monomers (G-actin). Traditionally, G-actin is thought to exist as a homogeneous pool. Here, we show that there are two functionally and molecularly distinct sources of G-actin that supply lamellipodial actin networks. G-actin originating from the cytosolic pool requires the monomer-binding protein thymosin β4 (Tβ4) for optimal leading-edge localization, is targeted to formins, and is responsible for creating an elevated G/F-actin ratio that promotes membrane protrusion. The second source of G-actin comes from recycled lamellipodia F-actin. Recycling occurs independently of Tβ4 and appears to regulate lamellipodia homeostasis. Tβ4-bound G-actin specifically localizes to the leading edge because it does not interact with Arp2/3-mediated polymerization sites found throughout the lamellipodia. These findings demonstrate that actin networks can be constructed from multiple sources of monomers with discrete spatiotemporal functions.

RhoA/mDia-1/profilin-1 signaling targets microvascular endothelial dysfunction in diabetic retinopathy

BACKGROUND

Diabetic retinopathy (DR) is a major cause of blindness in the working-age populations of developed countries, and effective treatments and prevention measures have long been the foci of study. Patients with DR invariably demonstrate impairments of the retinal microvascular endothelium. Many observational and preclinical studies have shown that angiogenesis and apoptosis play crucial roles in the pathogenesis of DR. Increasing evidence suggests that in DR, the small guanosine-5'-triphosphate-binding protein RhoA activates its downstream targets mammalian Diaphanous homolog 1 (mDia-1) and profilin-1, thus affecting important cellular functions, including cell morphology, motility, secretion, proliferation, and gene expression. However, the specific underlying mechanism of disease remains unclear.

CONCLUSION

This review focuses on the RhoA/mDia-1/profilin-1 signaling pathway that specifically triggers endothelial dysfunction in diabetic patients. Recently, RhoA and profilin-1 signaling has attracted a great deal of attention in the context of diabetes-related research. However, the precise molecular mechanism by which the RhoA/mDia-1/profilin-1 pathway is involved in progression of microvascular endothelial dysfunction (MVED) during DR has not been determined. This review briefly describes each feature of the cascade before exploring the most recent findings on how the pathway may trigger endothelial dysfunction in DR. When the underlying mechanisms are understood, novel therapies seeking to restore the endothelial homeostasis comprised in DR will become possible.

Identification of AMP-activated protein kinase targets by a consensus sequence search of the proteome

Background

AMP-activated protein kinase (AMPK) is a heterotrimeric serine/threonine protein kinase that is activated by cellular perturbations associated with ATP depletion or stress. While AMPK modulates the activity of a variety of targets containing a specific phosphorylation consensus sequence, the number of AMPK targets and their influence over cellular processes is currently thought to be limited.

Results

We queried the human and the mouse proteomes for proteins containing AMPK phosphorylation consensus sequences. Integration of this database into Gaggle software facilitated the construction of probable AMPK-regulated networks based on known and predicted molecular associations. In vitro kinase assays were conducted for preliminary validation of 12 novel AMPK targets across a variety of cellular functional categories, including transcription, translation, cell migration, protein transport, and energy homeostasis. Following initial validation, pathways that include NAD synthetase 1 (NADSYN1) and protein kinase B (AKT2) were hypothesized and experimentally tested to provide a mechanistic basis for AMPK regulation of cell migration and maintenance of cellular NAD⁺ concentrations during catabolic processes.

Conclusions

This study delineates an approach that encompasses both in silico procedures and in vitro experiments to produce testable hypotheses for AMPK regulation of cellular processes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12918-015-0156-0) contains supplementary material, which is available to authorized users.

Nestin-mediated cytoskeletal remodeling in endothelial cells: novel mechanistic insight into VEGF-induced cell migration in angiogenesis

Nestin is highly expressed in poorly differentiated and newly formed proliferating endothelial cells (ECs); however, the role of this protein in angiogenesis remains unknown. Additionally, the cytoskeleton and associated cytoskeleton-binding proteins mediate the migration of vascular ECs. Therefore, the aim of the present study was to determine whether VEGF regulates the cytoskeleton, as well as other associated proteins, to promote the migration of vascular ECs. The coexpression of nestin and CD31 during angiogenesis in alkali-burned rat corneas was examined via immunohistochemical analysis. Western blot analyses revealed that the exposure of human umbilical vein endothelial cells (HUVECs) to hypoxia promoted nestin expression in vitro. Additionally, nestin silencing via siRNA significantly inhibited many of the process associated with VEGF-induced angiogenesis, including tube formation and the migration and proliferation of HUVECs. Moreover, FITC-phalloidin labeling revealed that F-actin filaments were successfully organized into microfilaments in VEGF-treated cells, suggesting a network rearrangement accomplished via F-actin that contrasted with the uniform and loose actin filament network observed in the siRNA-nestin cells. The results of the present study highlight the key role played by nestin in activated HUVECs during angiogenesis. The inhibition of the ERK pathway suppressed the nestin expression induced by VEGF in the HUVECs. Therefore, our study provides the first evidence that nestin-mediated cytoskeleton remodeling in ECs occurs via filopodia formation along the cell edge, facilitating both filopodia localization and cell polarization and ultimately promoting HUVEC migration via VEGF induction, which may be associated with ERK pathway activation.

Controlled release of thymosin beta 4 using a collagen-chitosan sponge scaffold augments cutaneous wound healing and increases angiogenesis in diabetic rats with hindlimb ischemia

It is important to establish an efficient vascularization for the long-term acceptance of bioengineered skin equivalents treating the cutaneous wounds of diabetic rats with hindlimb ischemia. This study investigates the possible use of a collagen-chitosan sponge scaffold encapsulated with thymosin beta 4 (CCSS-eTβ4), an angiogenic factor, to accelerate cutaneous wound healing in streptozotocin (STZ)-induced diabetic rats with hindlimb ischemia. CCSSs-eTβ4 was fabricated using a freeze-drying method. The scaffolds were analyzed by scanning electron microscopy, swelling and degradation assays, mechanical properties, and scaffolds of 50:50 collagen-chitosan were selected and applied. The controlled release of Tβ4 from the scaffolds elicited localized and prolonged effects over 12 days, as shown by an enzyme-linked immunosorbent assay (ELISA). In vivo, CCSSs-eTβ4 improved diabetic cutaneous wound healing, with faster wound reepithelialization, better dermal reorganization, and higher wound vascularization. Furthermore, CCSSs-eTβ4 downregulated inflammatory genes and upregulated angiogenic genes in the wound tissue. Significant increases in CD31-positive endothelial cells and new vessel density were also observed. In vitro, Tβ4 increased the migratory and proliferative activity of high glucose (HG)-treated human umbilical vein endothelial cells (HUVECs). Meanwhile, we found that Tβ4 could promote HG-treated HUVECs migration and improve angiogenesis by activation of the VEGF/AKT pathway. Overall, these findings demonstrated the promising potential of CCSSs-eTβ4 to promote more effective wound healing and suggest its possible application for diabetic cutaneous wound treatment.

Thymosin β4 induces invasion and migration of human colorectal cancer cells through the ILK/AKT/β-catenin signaling pathway

Thymosin β4 (Tβ4) is a 43-amino-acid peptide involved in many biological processes. However, the precise molecular signaling mechanism(s) of Tβ4 in cell invasion and migration remain unclear. In this study, we show that Tβ4 was significantly overexpressed in colorectal cancer tissues compared to adjacent normal tissues and high levels of Tβ4 were correlated with stage of colorectal cancer, and that Tβ4 expression was associated with morphogenesis and EMT. Tβ4-upregulated cancer cells showed increased adhesion, invasion and migration activity, whereas Tβ4-downregulated cells showed decreased activities. We also demonstrated that Tβ4 interacts with ILK, which promoted the phosphorylation and activation of AKT, the phosphorylation and inactivation of GSK3β, the expression and nuclear localization of β-catenin, and integrin receptor activation. These results suggest that Tβ4 is an important regulator of the ILK/AKT/β-catenin/Integrin signaling cascade to induce cell invasion and migration in colorectal cancer cells, and is a potential target for cancer treatment.

Profilin-1 phosphorylation directs angiocrine expression and glioblastoma progression through HIF-1α accumulation

The tumour vascular microenvironment supports tumorigenesis not only by supplying oxygen and diffusible nutrients but also by secreting soluble factors that promote tumorigenesis. Here we identify a feedforward mechanism in which endothelial cells (ECs), in response to tumour-derived mediators, release angiocrines driving aberrant vascularization and glioblastoma multiforme (GBM) progression through a hypoxia-independent induction of hypoxia-inducible factor (HIF)-1α. Phosphorylation of profilin-1 (Pfn-1) at Tyr 129 in ECs induces binding to the tumour suppressor protein von Hippel-Lindau (VHL), and prevents VHL-mediated degradation of prolyl-hydroxylated HIF-1α, culminating in HIF-1α accumulation even in normoxia. Elevated HIF-1α induces expression of multiple angiogenic factors, leading to vascular abnormality and tumour progression. In a genetic model of GBM, mice with an EC-specific defect in Pfn-1 phosphorylation exhibit reduced tumour angiogenesis, normalized vasculature and improved survival. Moreover, EC-specific Pfn-1 phosphorylation is associated with tumour aggressiveness in human glioma. These findings suggest that targeting Pfn-1 phosphorylation may offer a selective strategy for therapeutic intervention of malignant solid tumours.

Thymosin β 4 gene silencing decreases stemness and invasiveness in glioblastoma

Thymosin beta 4 is a pleiotropic actin-sequestering polypeptide that is involved in wound healing and developmental processes. Thymosin beta 4 gene silencing promotes differentiation of neural stem cells whereas thymosin beta 4 overexpression initiates cortical folding of developing brain hemispheres. A role of thymosin beta 4 in malignant gliomas has not yet been investigated. We analysed thymosin beta 4 staining on tissue microarrays and performed interrogations of the REMBRANDT and the Cancer Genome Atlas databases. We investigated thymosin beta 4 expression in seven established glioma cell lines and seven glioma-initiating cell lines and induced or silenced thymosin beta 4 expression by lentiviral transduction in LNT-229, U87MG and GS-2 cells to study the effects of altered thymosin beta 4 expression on gene expression, growth, clonogenicity, migration, invasion, self-renewal and differentiation capacity in vitro, and tumorigenicity in vivo. Thymosin beta 4 expression increased with grade of malignancy in gliomas. Thymosin beta 4 gene silencing in LNT-229 and U87MG glioma cells inhibited migration and invasion, promoted starvation-induced cell death in vitro and enhanced survival of glioma-bearing mice. Thymosin beta 4 gene silencing in GS-2 cells inhibited self-renewal and promoted differentiation in vitro and decreased tumorigenicity in vivo. Gene expression analysis suggested a thymosin beta 4-dependent regulation of mesenchymal signature genes and modulation of TGFβ and p53 signalling networks. We conclude that thymosin beta 4 should be explored as a novel molecular target for anti-glioma therapy.

A novel dimeric thymosin beta 4 with enhanced activities accelerates the rate of wound healing

OBJECTIVE

Thymosin beta 4 (Tβ4) is a peptide with 43 amino acids that is critical for repair and remodeling tissues on the skin, eye, heart, and neural system following injury. To fully realize its utility as a treatment for disease caused by injury, the authors constructed a cost-effective novel Tβ4 dimer and demonstrated that it was better able to accelerate tissue repair than native Tβ4.

METHODS

A prokaryotic vector harboring two complete Tβ4 genes with a short linker was constructed and expressed in Escherichia coli. A pilot-scale fermentation (10 L) was performed to produce engineered bacteria and the Tβ4 dimer was purified by one-step hydrophobic interaction chromatography. The activities of the Tβ4 dimer to promote endothelial cell proliferation, migration, and sprouting were assessed by tetramethylbenzidine (methylthiazol tetrazolium), trans-well, scratch, and tube formation assays. The ability to accelerate dermal healing was assessed on rats.

RESULTS

After fermentation, the Tβ4 dimer accounted for about 30% of all the bacteria proteins. The purity of the Tβ4 dimer reached 98% after hydrophobic interaction chromatography purification. An average of 562.4 mg/L Tβ4 dimer was acquired using a 10 L fermenter. In each assay, the dimeric Tβ4 exhibited enhanced activities compared with native Tβ4. Notably, the ability of the dimeric Tβ4 to promote cell migration was almost two times higher than that of Tβ4. The rate of dermal healing in the dimeric Tβ4-treated rats was approximately 1 day faster than with native Tβ4-treated rats.

CONCLUSION

The dimeric Tβ4 exhibited enhanced activity on wound healing than native Tβ4, and the purification process was simple and cost-effective. This data could be of significant benefit for the high pain and morbidity associated with chronic wounds disease. A better strategy to develop Tβ4 as a treatment for other diseases caused by injuries such as heart attack, neurotrophic keratitis, and multiple sclerosis was also described.

Dynamic localization of G-actin during membrane protrusion in neuronal motility

BACKGROUND

Actin-based cell motility is fundamental for development, function, and malignant events in eukaryotic organisms. During neural development, axonal growth cones depend on rapid assembly and disassembly of actin filaments (F-actin) for their guided extension to specific targets for wiring. Monomeric globular actin (G-actin) is the building block for F-actin but is not considered to play a direct role in spatiotemporal control of actin dynamics in cell motility.

RESULTS

Here we report that a pool of G-actin dynamically localizes to the leading edge of growth cones and neuroblastoma cells to spatially elevate the G-/F-actin ratio that drives membrane protrusion and cell movement. Loss of G-actin localization leads to the cessation and retraction of membrane protrusions. Moreover, G-actin localization occurs asymmetrically in growth cones during attractive turning. Finally, we identify the actin monomer-binding proteins profilin and thymosin β4 as key molecules that localize actin monomers to the leading edge of lamellipodia for their motility.

CONCLUSIONS

Our results suggest that dynamic localization of G-actin provides a novel mechanism to regulate the spatiotemporal actin dynamics underlying membrane protrusion in cell locomotion and growth cone chemotaxis.

Thymosin β4 is not required for embryonic viability or vascular development

RATIONALE

Rossdeutsch et al describe a requirement for thymosin β4 (Tβ4) in vascular development. Impaired mural cell migration, differentiation, partial embryonic lethality, and hemorrhaging were observed after analysis of 2 lines of mice, one of which was germline null for Tβ4 and another in which Tβ4 was knocked down by endothelial-specific expression of Tβ4 short hairpin RNA. These data are in direct contrast to our published global and cardiac-specific Tβ4-knockout lines. Thus, the role of Tβ4 needs to be clarified to understand its importance in cardiovascular development.

OBJECTIVE

To investigate and clarify the role of Tβ4 in vascular smooth muscle cell development and vessel stability.

METHODS AND RESULTS

Examination of Tβ4 global knockouts did not demonstrate embryonic hemorrhaging, altered mural cell development, or lethality. Endothelial-specific knockouts also did not exhibit any embryonic lethality and were viable to adulthood.

CONCLUSIONS

Analysis of our Tβ4 global and cardiac- and endothelial-specific knockout models demonstrated that Tβ4 is dispensable for embryonic viability and vascular development.

Nanog suppresses cell migration by downregulating thymosin β4 and Rnd3

Nanog, Sox2, and Oct4 are key transcription factors critical for the pluripotency and self-renewal of embryonic stem (ES) cells. Their downregulations lead to differentiation, accompanied with changes in cell motility. Whether these factors impact cell motility directly, however, is not clear. Here we addressed this question by initially assessing their effect in non-stem cells. We found that the ectopic expression of Nanog, Sox2, or Oct4 markedly inhibited ECV304 cell migration. Detailed examinations revealed that Nanog induced disorganizations of the actin cytoskeleton and peripheral localizations of focal adhesions. These effects required its DNA-binding domain and are thus transcription dependent. Furthermore, thymosin β4 and Rnd3 were identified as its downstream targets. Their depletions in ECV304 cells by RNAi phenocopied the ectopic expression of Nanog in both cell motility and actin organization, whereas their ectopic expressions rescued the migration defect of Nanog overexpression. Both proteins were upregulated during mouse ES cell differentiation. Their levels in the pluripotent mouse P19 cells also increased upon Nanog ablation, coincident with an increase in cell motility. Moreover, persistent expression of Nanog in zebrafish embryos suppressed gastrulation and cell migration. These results indeed suggest a dual role of certain transcription factors in the orchestration of differentiation and motility.

Multiple fuzzy interactions in the moonlighting function of thymosin-β4

Thymosine β4 (Tß4) is a 43 amino acid long intrinsically disordered protein (IDP), which was initially identified as an actin-binding and sequestering molecule. Later it was described to have multiple other functions, such as regulation of endothelial cell differentiation, blood vessel formation, wound repair, cardiac cell migration, and survival.1 The various functions of Tβ4 are mediated by interactions with distinct and structurally unrelated partners, such as PINCH, ILK, and stabilin-2, besides the originally identified G-actin. Although the cellular readout of these interactions and the formation of these complexes have been thoroughly described, no attempt was made to study these interactions in detail, and to elucidate the thermodynamic, kinetic, and structural underpinning of this range of moonlighting functions. Because Tβ4 is mostly disordered, and its 4 described partners are structurally unrelated (the CTD of stabilin-2 is actually fully disordered), it occurred to us that this system might be ideal to characterize the structural adaptability and ensuing moonlighting functions of IDPs. Unexpectedly, we found that Tβ4 engages in multiple weak, transient, and fuzzy interactions, i.e., it is capable of mediating distinct yet specific interactions without adapting stable folded structures.

Myo1c facilitates G-actin transport to the leading edge of migrating endothelial cells

Addition of actin monomer (G-actin) to growing actin filaments (F-actin) at the leading edge generates force for cell locomotion. The polymerization reaction and its regulation have been studied in depth. However, the mechanism responsible for transport of G-actin substrate to the cell front is largely unknown; random diffusion, facilitated transport via myosin II contraction, local synthesis as a result of messenger ribonucleic acid localization, or F-actin turnover all might contribute. By tracking a photoactivatable, nonpolymerizable actin mutant, we show vectorial transport of G-actin in live migrating endothelial cells (ECs). Mass spectrometric analysis identified Myo1c, an unconventional F-actin-binding motor protein, as a major G-actin-interacting protein. The cargo-binding tail domain of Myo1c interacted with G-actin, and the motor domain was required for the transport. Local microinjection of Myo1c promoted G-actin accumulation and plasma membrane ruffling, and Myo1c knockdown confirmed its contribution to G-actin delivery to the leading edge and for cell motility. In addition, there is no obvious requirement for myosin II contractile-based transport of G-actin in ECs. Thus, Myo1c-facilitated G-actin transport might be a critical node for control of cell polarity and motility.

Stimulus-dependent phosphorylation of profilin-1 in angiogenesis

Angiogenesis, the formation of new blood vessels, is fundamental to development and post-injury tissue repair. Vascular endothelial growth factor (VEGF)-A guides and enhances endothelial cell migration to initiate angiogenesis. Profilin-1 (Pfn-1) is an actin-binding protein that enhances actin filament formation and cell migration, but stimulus-dependent regulation of Pfn-1 has not been observed. Here, we show that VEGF-A-inducible phosphorylation of Pfn-1 at Tyr 129 is critical for endothelial cell migration and angiogenesis. Chemotactic activation of VEGF receptor kinase-2 (VEGFR2) and Src induces Pfn-1 phosphorylation in the cell leading edge, promoting Pfn-1 binding to actin and actin polymerization. Conditional endothelial knock-in of phosphorylation-deficient Pfn1(Y129F) in mice reveals that Pfn-1 phosphorylation is critical for angiogenesis in response to wounding and ischaemic injury, but not for developmental angiogenesis. Thus, VEGFR2/Src-mediated phosphorylation of Pfn-1 bypasses canonical, multistep intracellular signalling events to initiate endothelial cell migration and angiogenesis, and might serve as a selective therapeutic target for anti-angiogenic therapy.

Omental grafting: a cell-based therapy for blood vessel repair

Clinicians regularly transplant omental pedicles to repair a wide variety of injured tissues, but the basic mechanism underlying this efficacious procedure is not understood. One possibility that has not been addressed is the ability of omentum to directly contribute regenerative cells to injured tissues. We hypothesized that if omental progenitor cells could be mobilized to incorporate into damaged tissue, the power of this therapy would be greatly expanded. Labelled omental grafts were transplanted into a murine carotid artery injury model. Selected grafts were treated with thymosin β4 (Tβ4) prior to transplantation to investigate the effects of chemical potentiation on healing. We found treatment of grafts with Tβ4-induced progenitor cells to fully integrate into the wall of injured vessels and differentiate into vascular smooth muscle. Myographic studies determined that arteries receiving Tβ4-stimulated grafts were functionally indistinguishable from uninjured controls. Concurrent in vitro analyses showed that Tβ4 promoted proliferation, migration and trans-differentiation of cells via AKT signalling. This study is the first to demonstrate that omentum can provide progenitor cells for repair, thus revealing a novel and naturally occurring source of vascular smooth muscle for use in cell-based therapies. Furthermore, our data show that this system can be optimized with inducing factors, highlighting a more powerful therapeutic potential than that of its current clinical application. This is a paradigm-setting concept that lays the foundation for the use of chemical genetics to enhance therapeutic outcomes in a myriad of fields.

Regenerative protein thymosin beta-4 is a novel regulator of purinergic signaling

By an unknown mechanism, β-thymosins are extracellular modulators of angiogenesis, inflammation, wound healing, and development. We were interested in identifying β-thymosin interactors and determining their importance in β-thymosins signaling in human vein endothelial cells (HUVECs). We performed pulldown experiments with biotinylated thymosin β-4 (Tβ4) in comparison to neutravidin beads alone and used mass spectrometric analysis to identify differentially interacting proteins. By this method, we identified F1-F0 ATP synthase, a known target of antiangiogenic angiostatin. By surface plasmon resonance, we determined for Tβ4 binding to the β subunit of ATP synthase a K(D) of 12 nM. Blocking antibodies and antagonists (oligomycin, IC(50) ∼1.8 μM; piceatannol, IC(50) ∼1.05 μM; and angiostatin, IC(50) ∼2.9 μg/ml) of ATP synthase inhibited the Tβ4-induced increase in cell surface ATP levels, as measured by luciferase assay, and the Tβ4-induced increase in HUVEC migration, as measured by transwell migration assay. Silencing of the ATP-responsive purinergic receptor P2X4 with siRNA also blocked Tβ4-induced HUVEC migration in a transwell assay. Furthermore, in silico we identified common amphiphilic α-helical structural similarities between β-thymosins and the inhibitory factor 1 (IF1), an inhibitor of ATP synthase hydrolysis. In summary, we have identified an extracellular signaling pathway where Tβ4 increases cell surface ATP levels via ATP synthase and have shown further that ATP-responsive P2X4 receptor is required for Tβ4-induced HUVEC migration.

Thymosin beta4 inhibits TNF-alpha-induced NF-kappaB activation, IL-8 expression, and the sensitizing effects by its partners PINCH-1 and ILK

The mechanisms by which thymosin β 4 (Tβ(4)) regulates the inflammatory response to injury are poorly understood. Previously, we demonstrated that ectopic Tβ(4) treatment inhibits injury-induced proinflammatory cytokine and chemokine production. We have also shown that Tβ(4) suppresses TNF-α-mediated NF-κB activation. Herein, we present novel evidence that Tβ(4) directly targets the NF-κB RelA/p65 subunit. We find that enforced expression of Tβ(4) interferes with TNF-α-mediated NF-κB activation, as well as downstream IL-8 gene transcription. These activities are independent of the G-actin-binding properties of Tβ(4). Tβ(4) blocks RelA/p65 nuclear translocation and targeting to the cognate κB site in the proximal region of the IL-8 gene promoter. Tβ(4) also inhibits the sensitizing effects of its intracellular binding partners, PINCH-1 and ILK, on NF-κB activity after TNF-α stimulation. The identification of a functional regulatory role by Tβ(4) and the focal adhesion proteins PINCH-1 and ILK on NF-κB activity in this study opens a new window for scientific exploration of how Tβ(4) modulates inflammation. In addition, the results of this study serve as a foundation for developing Tβ(4) as a new anti-inflammatory therapy.

ILK mediates the effects of strain on intestinal epithelial wound closure

The intestinal epithelium is subjected to repetitive deformation during normal gut function by peristalsis and villous motility. Such repetitive strain promotes intestinal epithelial migration across fibronectin in vitro, but signaling mediators for this are poorly understood. We hypothesized that integrin-linked kinase (ILK) mediates strain-stimulated migration in intestinal epithelial cells cultured on fibronectin. ILK kinase activity increased rapidly 5 min after strain induction in both Caco-2 and intestinal epithelial cell-6 (IEC-6) cells. Wound closure in response to strain was reduced in ILK small interfering RNA (siRNA)-transfected Caco-2 cell monolayers when compared with control siRNA-transfected Caco-2 cells. Pharmacological blockade of phosphatidylinositol-3 kinase (PI3K) or Src or reducing Src by siRNA prevented strain activation of ILK. ILK coimmunoprecipitated with focal adhesion kinase (FAK), and this association was decreased by mutation of FAK Tyr925 but not FAK Tyr397. Strain induction of FAK Tyr925 phosphorylation but not FAK Tyr397 or FAK Tyr576 phosphorylation was blocked in ILK siRNA-transfected cells. ILK-Src association was stimulated by strain and was blocked by the Src inhibitor PP2. Finally, ILK reduction by siRNA inhibited strain-induced phosphorylation of myosin light chain and Akt. These results suggest a strain-dependent signaling pathway in which ILK association with FAK and Src mediates the subsequent downstream strain-induced motogenic response and suggest that ILK induction by repetitive deformation may contribute to recovery from mucosal injury and restoration of the mucosal barrier in patients with prolonged ileus. ILK may therefore be an important target for intervention to maintain the mucosa in such patients.

Interaction of profilin-1 and F-actin via a β-arrestin-1/JNK signaling pathway involved in prostaglandin E(2)-induced human mesenchymal stem cells migration and proliferation

Although many previous reports have examined the function of prostaglandin E(2) (PGE(2)) in the migration and proliferation of various cell types, the role of the actin cytoskeleton in human mesenchymal stem cells (hMSCs) migration and proliferation has not been reported. The present study examined the involvement of profilin-1 (Pfn-1) and filamentous-actin (F-actin) in PGE(2)-induced hMSC migration and proliferation and its related signal pathways. PGE(2) (10(-6) M) increased both cell migration and proliferation, and also increased E-type prostaglandin receptor 2 (EP2) mRNA expression, β-arrestin-1 phosphorylation, and c-Jun N-terminal kinase (JNK) phosphorylation. Small interfering RNA (siRNA)-mediated knockdown of β-arrestin-1 and JNK (-1, -2, -3) inhibited PGE(2)-induced growth of hMSCs. PGE(2) also activated Pfn-1, which was blocked by JNK siRNA, and induced F-actin level and organization. Downregulation of Pfn-1 by siRNA decreased the level and organization of F-actin. In addition, specific siRNA for TRIO and F-actin-binding protein (TRIOBP) reduced the PGE(2)-induced increase in hMSC migration and proliferation. Together, these experimental data demonstrate that PGE(2) partially stimulates hMSCs migration and proliferation by interaction of Pfn-1 and F-actin via EP2 receptor-dependent β-arrestin-1/JNK signaling pathways.

Thymosins and muscle regeneration

Thymosins are a family of highly conserved small peptides originally isolated from calf thymus. One representative member of the family is thymosin-β₄ (Tβ₄), a major G-actin-sequestering peptide present in many tissues. In the last decade, various studies have uncovered several important functions for Tβ₄ related to the regeneration of injured tissues including skin and heart. In particular, Tβ₄ promotes endothelial cell migration via the activation of Akt2 kinase at the leading edge of the cell. In the case of skeletal muscle injury, increased levels of Tβ₄ are produced by muscle fibers and surrounding immune cells. Satellite cell-derived myoblasts and myocytes are chemoattracted by Tβ₄, which facilitates skeletal muscle regeneration. Recently, it was reported that Tβ₄ interacts physically with F₁-F₀ ATP synthase on the plasma membrane to increase the local concentration of ATP, which stimulates the P2X₄ purinergic receptor to elicit a migratory response from endothelial cells. Thus, it is clear that Tβ₄ is an important chemotactic factor involved in stem/progenitor cell-mediated tissue regeneration.

Thymosins β-4 and β-10 are expressed in bovine ovarian follicles and upregulated in cumulus cells during meiotic maturation

β-Thymosins are small proteins that regulate the actin cytoskeleton and are involved in cell motility, differentiation, the induction of metalloproteinases, in anti-inflammatory processes and tumourigenesis. However, their roles in the ovary have not yet been elucidated. Using transcriptomics and real time reverse transcription-polymerase chain reaction validation, the present study demonstrates that thymosin β-4 (TMSB4) and thymosin β-10 (TMSB10) are upregulated in bovine cumulus cells (CCs) during in vitro maturation of cumulus-oocyte complexes (COCs) in parallel with an increase in mRNA expression of HAS2, COX2 and PGR genes. Using immunocytochemistry, both proteins were found to be localised mainly in granulosa cells, CCs and oocytes, in both the cytoplasm and nucleus, as well as being colocalised with F-actin stress fibres in CCs. Using different maturation mediums, we showed that the expression of TMSB10, but not TMSB4, was positively correlated with COC expansion and progesterone secretion and negatively correlated with apoptosis. Immunofluorescence, coupled with terminal deoxyribonucleotidyl transferase-mediated dUTP-digoxigenin nick end-labelling (TUNEL), demonstrated the absence of TMSB4 and/or TMSB10 in apoptotic cells. TMSB10 expression was higher in COCs matured in vivo than in vitro, and differences related to the age of the animal were observed. TMSB4 and/or TMSB10 expression was unchanged, whereas HAS2 overexpressed in CCs from oocytes that developed to the blastocyst stage in vitro compared with those that did not. Thus, TMSB4 and/or TMSB10 ovarian expression patterns suggest that these two thymosins may be involved in cumulus modifications during maturation.

Systems microscopy approaches to understand cancer cell migration and metastasis

Cell migration is essential in a number of processes, including wound healing, angiogenesis and cancer metastasis. Especially, invasion of cancer cells in the surrounding tissue is a crucial step that requires increased cell motility. Cell migration is a well-orchestrated process that involves the continuous formation and disassembly of matrix adhesions. Those structural anchor points interact with the extra-cellular matrix and also participate in adhesion-dependent signalling. Although these processes are essential for cancer metastasis, little is known about the molecular mechanisms that regulate adhesion dynamics during tumour cell migration. In this review, we provide an overview of recent advanced imaging strategies together with quantitative image analysis that can be implemented to understand the dynamics of matrix adhesions and its molecular components in relation to tumour cell migration. This dynamic cell imaging together with multiparametric image analysis will help in understanding the molecular mechanisms that define cancer cell migration.