Expression and functional roles of angiopoietin-2 in skeletal muscles

KRAS mutation-driven angiopoietin 2 bestows anti-VEGF resistance in epithelial carcinomas

Defining reliable surrogate markers and overcoming drug resistance are the most challenging issues for improving therapeutic outcomes of antiangiogenic drugs (AADs) in cancer patients. At the time of this writing, no biomarkers are clinically available to predict AAD therapeutic benefits and drug resistance. Here, we uncovered a unique mechanism of AAD resistance in epithelial carcinomas with KRAS mutations that targeted angiopoietin 2 (ANG2) to circumvent antivascular endothelial growth factor (anti-VEGF) responses. Mechanistically, KRAS mutations up-regulated the FOXC2 transcription factor that directly elevated ANG2 expression at the transcriptional level. ANG2 bestowed anti-VEGF resistance as an alternative pathway to augment VEGF-independent tumor angiogenesis. Most colorectal and pancreatic cancers with KRAS mutations were intrinsically resistant to monotherapies of anti-VEGF or anti-ANG2 drugs. However, combination therapy with anti-VEGF and anti-ANG2 drugs produced synergistic and potent anticancer effects in KRAS-mutated cancers. Together, these data demonstrate that KRAS mutations in tumors serve as a predictive marker for anti-VEGF resistance and are susceptible to combination therapy with anti-VEGF and anti-ANG2 drugs.

Angiogenic ability of human endothelial cells was decreased following senescence induction with hydrogen peroxide: possible role of vegfr-2/akt-1 signaling pathway

Background

Many attempts are used to discover mechanisms driving impaired angiogenesis in age-related diseases. Angiogenesis is highly regulated by different signaling pathways. Here, we investigated the angiogenesis potential of human endothelial cells (ECs) upon exposure to hydrogen peroxide (H2O2), a cellular senescent factor.

Results

Data showed that the wound healing rate of HUVECs decreased upon incubation with H2O2 (P < 0.05). LOX activity and NO production were decreased in H2O2 treated cells (P < 0.05). Expression of miR-126 and VEGFR-2 up-regulated, while expression of miR-373 and HSP-70 up = regulated in H2O2 -induced cells (P < 0.05). In addition, we found that protein levels of p-Akt-1, VCAM-1, MMP-9, and IL-6 decreased in treated cells (P < 0.05).

Conclusions

Our data showed that H2O2 reduced the angiogenic response of HUVECs in vitro, which may be due to impairment of the VEGFR-2 signaling pathway.

Gene profiling in dorso-ventral patterning of mouse tongue development

BACKGROUND

The tongue is a muscular fleshy organ in the oral cavity that is anatomically divided into the dorsal, ventral, anterior, and posterior part. The intricate tissue organisation and diverse origins of the tongue make it a complex organ of the oral cavity.

OBJECTIVES

To reveal the signalling molecules involved in the formation of the dorsal and ventral parts of the tongue through microarray analysis.

METHODS

Dorsal and ventral tongue tissues were isolated from embryonic day 14 mice by micro-dissection. RNA was extracted from the dorsal and ventral tongue tissues separately for microarray analysis. Microarray data were confirmed by quantitative reverse transcription polymerase chain reaction and whole-mount in situ hybridisation.

RESULTS

Microarray analysis revealed expression of 33,793 genes. Of these, 931 genes were found to be equally expressed in both the dorsal and ventral parts of the tongue. On limiting the fold-change cut-off to over 1.5-fold, 725 genes were expressed over 1.5-fold in the ventral part and 1,672 in the dorsal part of the tongue. The qPCR and whole-mount in situ hybridisation revealed the expressions of angiopoietin 2 (Angpt2), fibroblast growth factor 18 (Fgf18), mesenchyme homeobox gene1 (Meox1), and SPARC-related modular calcium binding 2 (Smoc2) in the ventral part of the tongue.

CONCLUSIONS

Numerous signalling molecules can be selected from our microarray results to examine their roles in tongue development and disease model systems. In the near future, the selection of candidate genes and their functional evaluations will be performed through loss- and gain-of-function mutation studies.

Angiopoietin-2-induced lymphatic endothelial cell migration drives lymphangiogenesis via the β1 integrin-RhoA-formin axis

Lymphangiogenesis is an essential physiological process but also a determining factor in vascular-related pathological conditions. Angiopoietin-2 (Ang2) plays an important role in lymphatic vascular development and function and its upregulation has been reported in several vascular-related diseases, including cancer. Given the established role of the small GTPase RhoA on cytoskeleton-dependent endothelial functions, we investigated the relationship between RhoA and Ang2-induced cellular activities. This study shows that Ang2-driven human dermal lymphatic endothelial cell migration depends on RhoA. We demonstrate that Ang2-induced migration is independent of the Tie receptors, but dependent on β1 integrin-mediated RhoA activation with knockdown, pharmacological approaches, and protein sequencing experiments. Although the key proteins downstream of RhoA, Rho kinase (ROCK) and myosin light chain, were activated, blockade of ROCK did not abrogate the Ang2-driven migratory effect. However, formins, an alternative target of RhoA, were identified as key players, and especially FHOD1. The Ang2-RhoA relationship was explored in vivo, where lymphatic endothelial RhoA deficiency blocked Ang2-induced lymphangiogenesis, highlighting RhoA as an important target for anti-lymphangiogenic treatments.

Transcriptomic adaptation during skeletal muscle habituation to eccentric or concentric exercise training

Eccentric (ECC) and concentric (CON) contractions induce distinct muscle remodelling patterns that manifest early during exercise training, the causes of which remain unclear. We examined molecular signatures of early contraction mode-specific muscle adaptation via transcriptome-wide network and secretome analyses during 2 weeks of ECC- versus CON-specific (downhill versus uphill running) exercise training (exercise 'habituation'). Despite habituation attenuating total numbers of exercise-induced genes, functional gene-level profiles of untrained ECC or CON were largely unaltered post-habituation. Network analysis revealed 11 ECC-specific modules, including upregulated extracellular matrix and immune profiles plus downregulated mitochondrial pathways following untrained ECC. Of 3 CON-unique modules, 2 were ribosome-related and downregulated post-habituation. Across training, 376 ECC-specific and 110 CON-specific hub genes were identified, plus 45 predicted transcription factors. Secreted factors were enriched in 3 ECC- and/or CON-responsive modules, with all 3 also being under the predicted transcriptional control of SP1 and KLF4. Of 34 candidate myokine hubs, 1 was also predicted to have elevated expression in skeletal muscle versus other tissues: THBS4, of a secretome-enriched module upregulated after untrained ECC. In conclusion, distinct untrained ECC and CON transcriptional responses are dampened after habituation without substantially shifting molecular functional profiles, providing new mechanistic candidates into contraction-mode specific muscle regulation.

Modeling of endothelial cell dysfunction using human induced pluripotent stem cells derived from patients with end-stage renal disease

Background

Endothelial cell (EC) dysfunction is a frequent feature in patients with end-stage renal disease (ESRD). The aim of this study was to generate human induced pluripotent stem cells, differentiate ECs (hiPSC-ECs) from patients with ESRD, and appraise the usefulness of hiPSC-ECs as a model to investigate EC dysfunction.

Methods

We generated hiPSCs using peripheral blood mononuclear cells (PBMCs) isolated from three patients with ESRD and three healthy controls (HCs). Next, we differentiated hiPSC-ECs using the generated hiPSCs and assessed the expression of endothelial markers by immunofluorescence. The differentiation efficacy, EC dysfunction, and molecular signatures of EC-related genes based on microarray analysis were compared between the ESRD and HC groups.

Results

In both groups, hiPSCs and hiPSC-ECs were successfully obtained based on induced pluripotent stem cell or EC marker expression in immunofluorescence and flow cytometry. However, the efficiency of differentiation of ECs from hiPSCs was lower in the ESRD-hiPSCs than in the HC-hiPSCs. In addition, unlike HC-hiPSC-ECs, ESRD-hiPSC-ECs failed to form interconnecting branching point networks in an in vitro tube formation assay. During microarray analysis, transcripts associated with oxidative stress and inflammation were upregulated and transcripts associated with vascular development and basement membrane extracellular matrix components were downregulated in ESRD-hiPSC-ECs relative to in HC-hiPSC-ECs.

Conclusion

ESRD-hiPSC-ECs showed a greater level of EC dysfunction than HC-hiPSC-ECs did based on functional assay results and molecular profiles. hiPSC-ECs may be used as a disease model to investigate the pathophysiology of EC dysfunction in ESRD.

ETS1, ELK1, and ETV4 Transcription Factors Regulate Angiopoietin-1 Signaling and the Angiogenic Response in Endothelial Cells

Background

Angiopoietin-1 (Ang-1) is the main ligand of Tie-2 receptors. It promotes endothelial cell (EC) survival, migration, and differentiation. Little is known about the transcription factors (TFs) in ECs that are downstream from Tie-2 receptors.

Objective

The main objective of this study is to identify the roles of the ETS family of TFs in Ang-1 signaling and the angiogenic response.

Methods

In silico enrichment analyses that were designed to predict TF binding sites of the promotors of eighty-six Ang-1-upregulated genes showed significant enrichment of ETS1, ELK1, and ETV4 binding sites in ECs. Human umbilical vein endothelial cells (HUVECs) were exposed for different time periods to recombinant Ang-1 protein and mRNA levels of ETS1, ELK1, and ETV4 were measured with qPCR and intracellular localization of these transcription factors was assessed with immunofluorescence. Electrophoretic mobility shift assays and reporter assays were used to assess activation of ETS1, ELK1, and ETV4 in response to Ang-1 exposure. The functional roles of these TFs in Ang-1-induced endothelial cell survival, migration, differentiation, and gene regulation were evaluated by using a loss-of-function approach (transfection with siRNA oligos).

Results

Ang-1 exposure increased ETS1 mRNA levels but had no effect on ELK1 or ETV4 levels. Immunostaining revealed that in control ECs, ETS1 has nuclear localization whereas ELK1 and ETV4 are localized to the nucleus and the cytosol. Ang-1 exposure increased nuclear intensity of ETS1 protein and enhanced nuclear mobilization of ELK1 and ETV4. Selective siRNA knockdown of ETS1, ELK1, and ETV4 showed that these TFs are required for Ang-1-induced EC survival and differentiation of cells, while ETS1 and ETV4 are required for Ang-1-induced EC migration. Moreover, ETS1, ELK1, and ETV4 knockdown inhibited Ang-1-induced upregulation of thirteen, eight, and nine pro-angiogenesis genes, respectively.

Conclusion

We conclude that ETS1, ELK1, and ETV4 transcription factors play significant angiogenic roles in Ang-1 signaling in ECs.

Endothelial cells response to neutrophil-derived extracellular vesicles miRNAs in anti-PR3 positive vasculitis

In vasculitis disorders, inflammation affects blood vessels. Granulomatosis with polyangiitis (GPA) is a chronic systemic vasculitis distinguished by the presence of anti-proteinase-3 autoantibodies (anti-PR3). In this study we analyzed the molecular signature of human umbilical endothelial cells (HUVECs) in response to neutrophil-derived extracellular vesicles (EVs). EVs were obtained from anti-PR3-activated neutrophils, purified and characterized by flow cytometry, nanoparticle tracking and miRNA screening. HUVECs were stimulated with EVs and miRNA/mRNA expression was measured. Cell culture media proteins were identified by antibody microarrays and selected cytokines were measured. Comparison of differentially expressed miRNAs/mRNAs between non-stimulated and EV-stimulated HUVECs revealed two regulatory patterns. Significant up-regulation of 14 mRNA transcripts (including CXCL8, DKK1, IL1RL1, ANGPT-2, THBS1 and VCAM-1) was accompanied by 11 miRNAs silencing (including miR-661, miR-664a-3p, miR-377-3p, miR-30d-5p). Significant down-regulation was observed for nine mRNA transcripts (including FASLG, CASP8, STAT3, GATA3, IRAK1 and IL6) and accompanied by up-regulation of 10 miRNAs (including miR-223-3p, miR-142-3p, miR-211-5p). Stimulated HUVECs released IL-8, Dickkopf-related protein 1 (DKK-1), soluble interleukin (IL)-1 like receptor-1 (ST2), growth differentiation factor 15 (GDF-15), angiopoietin-2, endoglin, thrombospondin-1 and vascular adhesion molecule-1 (VCAM-1). Moreover, transfection of HUVECs with mimics of highly expressed in EVs miR-223-3p or miR-142-3p, stimulated production of IL-8, ST2 and endoglin. Cytokines released by HUVECs were also elevated in blood of patients with GPA. The most increased were IL-8, DKK-1, ST2, angiopoietin-2 and IL-33. In-vitro stimulation of HUVECs by neutrophil-derived EVs recapitulates contribution of endothelium in autoimmune vasculitis. Proinflammatory phenotype of released cytokines corresponds with the regulatory network of miRNAs/mRNAs comprising both EVs miRNA and endothelial cell transcripts.

Upstream Regulator Analysis of Wooden Breast Myopathy Proteomics in Commercial Broilers and Comparison to Feed Efficiency Proteomics in Pedigree Male Broilers

In an effort to understand the apparent trade-off between the continual push for growth performance and the recent emergence of muscle pathologies, shotgun proteomics was conducted on breast muscle obtained at ~8 weeks from commercial broilers with wooden breast (WB) myopathy and compared with that in pedigree male (PedM) broilers exhibiting high feed efficiency (FE). Comparison of the two proteomic datasets was facilitated using the overlay function of Ingenuity Pathway Analysis (IPA) (Qiagen, CA, USA). We focused on upstream regulator analysis and disease-function analysis that provides predictions of activation or inhibition of molecules based on (a) expression of downstream target molecules, (b) the IPA scientific citation database. Angiopoeitin 2 (ANGPT2) exhibited the highest predicted activation Z-score of all molecules in the WB dataset, suggesting that the proteomic landscape of WB myopathy would promote vascularization. Overlaying the FE proteomics data on the WB ANGPT2 upstream regulator network presented no commonality of protein expression and no prediction of ANGPT2 activation. Peroxisome proliferator coactivator 1 alpha (PGC1α) was predicted to be inhibited, suggesting that mitochondrial biogenesis was suppressed in WB. PGC1α was predicted to be activated in high FE pedigree male broilers. Whereas RICTOR (rapamycin independent companion of mammalian target of rapamycin) was predicted to be inhibited in both WB and FE datasets, the predictions were based on different downstream molecules. Other transcription factors predicted to be activated in WB muscle included epidermal growth factor (EGFR), X box binding protein (XBP1), transforming growth factor beta 1 (TGFB1) and nuclear factor (erythroid-derived 2)-like 2 (NFE2L2). Inhibitions of aryl hydrocarbon receptor (AHR), AHR nuclear translocator (ARNT) and estrogen related receptor gamma (ESRRG) were also predicted in the WB muscle. These findings indicate that there are considerable differences in upstream regulators based on downstream protein expression observed in WB myopathy and in high FE PedM broilers that may provide additional insight into the etiology of WB myopathy.

Platelet releasate promotes skeletal myogenesis by increasing muscle stem cell commitment to differentiation and accelerates muscle regeneration following acute injury

AIM

The use of platelets as biomaterials has gained intense research interest. However, the mechanisms regarding platelet-mediated skeletal myogenesis remain to be established. The aim of this study was to determine the role of platelet releasate in skeletal myogenesis and muscle stem cell fate in vitro and ex vivo respectively.

METHODS

We analysed the effect of platelet releasate on proliferation and differentiation of C2C12 myoblasts by means of cell proliferation assays, immunohistochemistry, gene expression and cell bioenergetics. We expanded in vitro findings on single muscle fibres by determining the effect of platelet releasate on murine skeletal muscle stem cells using protein expression profiles for key myogenic regulatory factors.

RESULTS

TRAP6 and collagen used for releasate preparation had a more pronounced effect on myoblast proliferation vs thrombin and sonicated platelets (P < 0.05). In addition, platelet concentration positively correlated with myoblast proliferation. Platelet releasate increased myoblast and muscle stem cell proliferation in a dose-dependent manner, which was mitigated by VEGFR and PDGFR inhibition. Inhibition of VEGFR and PDGFR ablated MyoD expression on proliferating muscle stem cells, compromising their commitment to differentiation in muscle fibres (P < 0.001). Platelet releasate was detrimental to myoblast fusion and affected differentiation of myoblasts in a temporal manner. Most importantly, we show that platelet releasate promotes skeletal myogenesis through the PDGF/VEGF-Cyclin D1-MyoD-Scrib-Myogenin axis and accelerates skeletal muscle regeneration after acute injury.

CONCLUSION

This study provides novel mechanistic insights on the role of platelet releasate in skeletal myogenesis and set the physiological basis for exploiting platelets as biomaterials in regenerative medicine.

A focus on extracellular Ca2+ entry into skeletal muscle

The main task of skeletal muscle is contraction and relaxation for body movement and posture maintenance. During contraction and relaxation, Ca²⁺ in the cytosol has a critical role in activating and deactivating a series of contractile proteins. In skeletal muscle, the cytosolic Ca²⁺ level is mainly determined by Ca²⁺ movements between the cytosol and the sarcoplasmic reticulum. The importance of Ca²⁺ entry from extracellular spaces to the cytosol has gained significant attention over the past decade. Store-operated Ca²⁺ entry with a low amplitude and relatively slow kinetics is a main extracellular Ca²⁺ entryway into skeletal muscle. Herein, recent studies on extracellular Ca²⁺ entry into skeletal muscle are reviewed along with descriptions of the proteins that are related to extracellular Ca²⁺ entry and their influences on skeletal muscle function and disease.

Combining a micro/nano-hierarchical scaffold with cell-printing of myoblasts induces cell alignment and differentiation favorable to skeletal muscle tissue regeneration

Biomedical scaffolds must be used in tissue engineering to provide physical stability and topological/biochemical properties that directly affect tissue regeneration. In this study, a new cell-laden scaffold was developed that supplies micro/nano-topological cues and promotes efficient release of cells. The hierarchical structure consisted of poly(ε-caprolactone) macrosized struts for sustaining a three-dimensional structural shape, aligned nanofibers obtained with optimized electrospinning, and cell-printed myoblasts. Importantly, the printed myoblasts were fully safe and were efficiently released from the cell-laden struts to neighboring nanofiber networks. The incorporation of micro/nanofibers in the hierarchical scaffold significantly affected myoblast proliferation, alignment, and even facilitated the formation of myotubes. We observed that myosin heavy chain expression and the expression levels of various myogenic genes (MyoD, myogenin, and troponin T) were significantly affected by the fiber alignment achieved in our hierarchical cell-laden structure. We believe that the combination of cell-printing and a hierarchical scaffold that encourages fiber alignment is a highly promising technique for skeletal muscle tissue engineering.

Heat therapy promotes the expression of angiogenic regulators in human skeletal muscle

Heat therapy has been shown to promote capillary growth in skeletal muscle and in the heart in several animal models, but the effects of this therapy on angiogenic signaling in humans are unknown. We evaluated the acute effect of lower body heating (LBH) and unilateral thigh heating (TH) on the expression of angiogenic regulators and heat shock proteins (HSPs) in healthy young individuals. Exposure to LBH (n = 18) increased core temperature (Tc) from 36.9 ± 0.1 to 37.4 ± 0.1°C (P < 0.01) and average leg skin temperature (Tleg) from 33.1 ± 0.1 to 39.6 ± 0.1°C (P < 0.01), but did not alter the levels of circulating angiogenic cytokines and bone marrow-derived proangiogenic cells (CD34(+)CD133(+)). In skeletal muscle, the change in mRNA expression from baseline of vascular endothelial growth factor (VEGF), angiopoietin 2 (ANGPT2), chemokines CCL2 and CX3CL1, platelet factor-4 (PF4), and several members of the HSP family was higher 30 min after the intervention in the individuals exposed to LBH (n = 11) compared with the control group (n = 12). LBH also reduced the expression of transcription factor FOXO1 (P = 0.03). Exposure to TH (n = 14) increased Tleg from 32.8 ± 0.2 to 40.3 ± 0.1°C (P < 0.05) but Tc remained unaltered (36.8 ± 0.1°C at baseline and 36.9 ± 0.1°C at 90 min). This intervention upregulated the expression of VEGF, ANGPT1, ANGPT2, CCL2, and HSPs in skeletal muscle but did not affect the levels of CX3CL1, FOXO-1, and PF4. These findings suggest that both LBH and TH increase the expression of factors associated with capillary growth in human skeletal muscle.

Role of Growth Factors in Modulation of the Microvasculature in Adult Skeletal Muscle

Post-natal skeletal muscle is a highly plastic tissue that has the capacity to regenerate rapidly following injury, and to undergo significant modification in tissue mass (i.e. atrophy/hypertrophy) in response to global metabolic changes. These processes are reliant largely on soluble factors that directly modulate muscle regeneration and mass. However, skeletal muscle function also depends on an adequate blood supply. Thus muscle regeneration and changes in muscle mass, particularly hypertrophy, also demand rapid changes in the microvasculature. Recent evidence clearly demonstrates a critical role for soluble growth factors in the tight regulation of angiogenic expansion of the muscle microvasculature. Furthermore, exogenous modulation of these factors has the capacity to impact directly on angiogenesis and thus, indirectly, on muscle regeneration, growth and performance. This chapter reviews recent developments in understanding the role of growth factors in modulating the skeletal muscle microvasculature, and the potential therapeutic applications of exogenous angiogenic and anti-angiogenic mediators in promoting effective growth and regeneration, and ameliorating certain diseases, of skeletal muscle.

Transcriptional Profiling Identifies Location-Specific and Breed-Specific Differentially Expressed Genes in Embryonic Myogenesis in Anas Platyrhynchos

Skeletal muscle growth and development are highly orchestrated processes involving significant changes in gene expressions. Differences in the location-specific and breed-specific genes and pathways involved have important implications for meat productions and meat quality. Here, RNA-Seq was performed to identify differences in the muscle deposition between two muscle locations and two duck breeds for functional genomics studies. To achieve those goals, skeletal muscle samples were collected from the leg muscle (LM) and the pectoral muscle (PM) of two genetically different duck breeds, Heiwu duck (H) and Peking duck (P), at embryonic 15 days. Functional genomics studies were performed in two experiments: Experiment 1 directly compared the location-specific genes between PM and LM, and Experiment 2 compared the two breeds (H and P) at the same developmental stage (embryonic 15 days). Almost 13 million clean reads were generated using Illumina technology (Novogene, Beijing, China) on each library, and more than 70% of the reads mapped to the Peking duck (Anas platyrhynchos) genome. A total of 168 genes were differentially expressed between the two locations analyzed in Experiment 1, whereas only 8 genes were differentially expressed when comparing the same location between two breeds in Experiment 2. Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes pathways (KEGG) were used to functionally annotate DEGs (differentially expression genes). The DEGs identified in Experiment 1 were mainly involved in focal adhesion, the PI3K-Akt signaling pathway and ECM-receptor interaction pathways (corrected P-value<0.05). In Experiment 2, the DEGs were associated with only the ribosome signaling pathway (corrected P-value<0.05). In addition, quantitative real-time PCR was used to confirm 15 of the differentially expressed genes originally detected by RNA-Seq. A comparative transcript analysis of the leg and pectoral muscles of two duck breeds not only improves our understanding of the location-specific and breed-specific genes and pathways but also provides some candidate molecular targets for increasing muscle products and meat quality by genetic control.

Angiopoietin-1 enhances skeletal muscle regeneration in mice

Activation of muscle progenitor cell myogenesis and endothelial cell angiogenesis is critical for the recovery of skeletal muscle from injury. Angiopoietin-1 (Ang-1), a ligand of Tie-2 receptors, enhances angiogenesis and skeletal muscle satellite cell survival; however, its role in skeletal muscle regeneration after injury is unknown. We assessed the effects of Ang-1 on fiber regeneration, myogenesis, and angiogenesis in injured skeletal muscle (tibialis anterior, TA) in mice. We also assessed endogenous Ang-1 levels and localization in intact and injured TA muscles. TA fiber injury was triggered by cardiotoxin injection. Endogenous Ang-1 mRNA levels immediately decreased in response to cardiotoxin then increased during the 2 wk. Ang-1 protein was expressed in satellite cells, both in noninjured and recovering TA muscles. Positive Ang-1 staining was present in blood vessels but not in nerve fibers. Four days after the initiation of injury, injection of adenoviral Ang-1 into injured muscles resulted in significant increases in in situ TA muscle contractility, muscle fiber regeneration, and capillary density. In cultured human skeletal myoblasts, recombinant Ang-1 protein increased survival, proliferation, migration, and differentiation into myotubes. The latter effect was associated with significant upregulation of the expression of the myogenic regulatory factors MyoD and Myogenin and certain genes involved in cell cycle regulation. We conclude that Ang-1 strongly enhances skeletal muscle regeneration in response to fiber injury and that this effect is mediated through induction of the myogenesis program in muscle progenitor cells and the angiogenesis program in endothelial cells.

DNA methylation analysis of human myoblasts during in vitro myogenic differentiation: de novo methylation of promoters of muscle-related genes and its involvement in transcriptional down-regulation

Although DNA methylation is considered to play an important role during myogenic differentiation, chronological alterations in DNA methylation and gene expression patterns in this process have been poorly understood. Using the Infinium HumanMethylation450 BeadChip array, we obtained a chronological profile of the genome-wide DNA methylation status in a human myoblast differentiation model, where myoblasts were cultured in low-serum medium to stimulate myogenic differentiation. As the differentiation of the myoblasts proceeded, their global DNA methylation level increased and their methylation patterns became more distinct from those of mesenchymal stem cells. Gene ontology analysis revealed that genes whose promoter region was hypermethylated upon myoblast differentiation were highly significantly enriched with muscle-related terms such as 'muscle contraction' and 'muscle system process'. Sequence motif analysis identified 8-bp motifs somewhat similar to the binding motifs of ID4 and ZNF238 to be most significantly enriched in hypermethylated promoter regions. ID4 and ZNF238 have been shown to be critical transcriptional regulators of muscle-related genes during myogenic differentiation. An integrated analysis of DNA methylation and gene expression profiles revealed that de novo DNA methylation of non-CpG island (CGI) promoters was more often associated with transcriptional down-regulation than that of CGI promoters. These results strongly suggest the existence of an epigenetic mechanism in which DNA methylation modulates the functions of key transcriptional factors to coordinately regulate muscle-related genes during myogenic differentiation.

Angiopoietin-1 and angiopoietin-2 are altered in polycystic ovarian syndrome (PCOS) during controlled ovarian stimulation

Polycystic ovarian syndrome (PCOS) ovaries are characterized by increased angiogenesis and hypervascularity. While angiopoietin-1 (Ang-1) and its antagonist, angiopoietin-2 (Ang-2), are essential for ovarian function and angiogenesis, the levels of Ang-1 and Ang-2 in PCOS are unknown. This was a prospective cohort study of 14 PCOS women and 14 matched controls undergoing controlled ovarian stimulation (COS). Serum was collected on day 3, hCG and retrieval days. Follicular fluid (FF) was collected on retrieval day. Serum Ang-1 and Ang-2 levels were constant throughout COS, but serum Ang-1 levels were increased at all time points in PCOS women compared with controls (p < 0.05). No differences between groups were found in serum Ang-2 levels or FF Ang-1 levels. However, FF Ang-2 levels were increased almost 2-fold in PCOS women compared with controls (p < 0.01), and correlated positively with number of oocytes retrieved (r = 0.65, p < 0.0001). This study is the first to provide evidence of an alteration in the Ang-1/Ang-2 system in PCOS women. The biological role of Ang-2 in promoting capillary leakage, the increased Ang-2 FF level in PCOS, and its correlation with number of oocytes suggest that Ang-2 may play an important role in the increased risk of ovarian hyperstimulation in PCOS.

Angiopoietin 1 enhances the proliferation and differentiation of skeletal myoblasts

Angiopoietin 1 (Ang1) plays an important role in various endothelial functions, such as vascular integrity and angiogenesis; however, less is known about its function outside of the endothelium. In this study, we examined whether Ang1 has direct effects on skeletal muscle cells. We found that Ang1 exhibited myogenic potential, as it promoted the proliferation, migration, and differentiation of mouse primary skeletal myoblasts. The positive effect of Ang1 on myoblast proliferation could have been mediated by the α7 and β1 integrins. We also found that Ang1 potentiated cellular Ca(2+) movements in differentiated myotubes in response to stimuli, possibly through the increased expression of two Ca(2+) -related proteins, namely, Orai1 and calmodulin. Ang1 also increased Orai1 and calmodulin expression in mouse hearts in vivo. These results provide an insight into the molecular mechanisms by which Ang1 directly affects the myogenesis of striated muscle.

Oxygen consumption and usage during physical exercise: the balance between oxidative stress and ROS-dependent adaptive signaling

The complexity of human DNA has been affected by aerobic metabolism, including endurance exercise and oxygen toxicity. Aerobic endurance exercise could play an important role in the evolution of Homo sapiens, and oxygen was not important just for survival, but it was crucial to redox-mediated adaptation. The metabolic challenge during physical exercise results in an elevated generation of reactive oxygen species (ROS) that are important modulators of muscle contraction, antioxidant protection, and oxidative damage repair, which at moderate levels generate physiological responses. Several factors of mitochondrial biogenesis, such as peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α), mitogen-activated protein kinase, and SIRT1, are modulated by exercise-associated changes in the redox milieu. PGC-1α activation could result in decreased oxidative challenge, either by upregulation of antioxidant enzymes and/or by an increased number of mitochondria that allows lower levels of respiratory activity for the same degree of ATP generation. Endogenous thiol antioxidants glutathione and thioredoxin are modulated with high oxygen consumption and ROS generation during physical exercise, controlling cellular function through redox-sensitive signaling and protein-protein interactions. Endurance exercise-related angiogenesis, up to a significant degree, is regulated by ROS-mediated activation of hypoxia-inducible factor 1α. Moreover, the exercise-associated ROS production could be important to DNA methylation and post-translation modifications of histone residues, which create heritable adaptive conditions based on epigenetic features of chromosomes. Accumulating data indicate that exercise with moderate intensity has systemic and complex health-promoting effects, which undoubtedly involve regulation of redox homeostasis and signaling.

Angiogenesis-related factors in skeletal muscles of COPD patients: roles of angiopoietin-2

The role of angiogenesis factors in skeletal muscle dysfunction in patients with chronic obstructive pulmonary disease (COPD) is unknown. The first objective of this study was to assess various pro- and antiangiogenic factor and receptor expressions in the vastus lateralis muscles of control subjects and COPD patients. Preliminary inquiries revealed that angiopoietin-2 (ANGPT2) is overexpressed in limb muscles of COPD patients. ANGPT2 promotes skeletal satellite cell survival and differentiation. Factors that are involved in regulating muscle ANGPT2 production are unknown. The second objective of this study was to evaluate how oxidants and proinflammatory cytokines influence muscle-derived ANGPT2 expression. Angiogenic gene expressions in human vastus lateralis biopsies were quantified with low-density real-time PCR arrays. ANGPT2 mRNA expressions in cultured skeletal myoblasts were quantified in response to proinflammatory cytokine and H2O2 exposure. Ten proangiogenesis genes, including ANGPT2, were significantly upregulated in the vastus lateralis muscles of COPD patients. ANGPT2 mRNA levels correlated negatively with forced expiratory volume in 1 s and positively with muscle wasting. Immunoblotting confirmed that ANGPT2 protein levels were significantly greater in muscles of COPD patients compared with control subjects. ANGPT2 expression was induced by interferon-γ and -β and by hydrogen peroxide, but not by tumor necrosis factor. We conclude that upregulation of ANGPT2 expression in vastus lateralis muscles of COPD patients is likely due to oxidative stress and represents a positive adaptive response aimed at facilitating myogenesis and angiogenesis.

Functional consequences of prolactin signalling in endothelial cells: a potential link with angiogenesis in pathophysiology?

Prolactin is best known as the polypeptide anterior pituitary hormone, which regulates the development of the mammary gland. However, it became clear over the last decade that prolactin contributes to a broad range of pathologies, including breast cancer. Prolactin is also involved in angiogenesis via the release of pro-angiogenic factors by leukocytes and epithelial cells. However, whether prolactin also influences endothelial cells, and whether there are functional consequences of prolactin-induced signalling in the perspective of angiogenesis, remains so far elusive. In the present study, we show that prolactin induces phosphorylation of ERK1/2 and STAT5 and induces tube formation of endothelial cells on Matrigel. These effects are blocked by a specific prolactin receptor antagonist, del1-9-G129R-hPRL. Moreover, in an in vivo model of the chorioallantoic membrane of the chicken embryo, prolactin enhances vessel density and the tortuosity of the vasculature and pillar formation, which are hallmarks of intussusceptive angiogenesis. Interestingly, while prolactin has only little effect on endothelial cell proliferation, it markedly stimulates endothelial cell migration. Again, migration was reverted by del1-9-G129R-hPRL, indicating a direct effect of prolactin on its receptor. Immunohistochemistry and spectral imaging revealed that the prolactin receptor is present in the microvasculature of human breast carcinoma tissue. Altogether, these results suggest that prolactin may directly stimulate angiogenesis, which could be one of the mechanisms by which prolactin contributes to breast cancer progression, thereby providing a potential tool for intervention.