Heparin-binding epidermal growth factor-like growth factor, collateral vessel development, and angiogenesis in skeletal muscle ischemia

Integrating miRNA and full-length transcriptome profiling to elucidate the mechanism of muscle growth in Muscovy ducks reveals key roles for miR-301a-3p/ANKRD1

BACKGROUND

The popularity of Muscovy ducks is attributed not only to their conformation traits but also to their slightly higher content of breast and leg meat, as well as their stronger-tasting meat compared to that of typical domestic ducks. However, there is a lack of comprehensive systematic research on the development of breast muscle in Muscovy ducks. In addition, since the number of skeletal muscle myofibers is established during the embryonic period, this study conducted a full-length transcriptome sequencing and microRNA sequencing of the breast muscle. Muscovy ducks at four developmental stages, namely Embryonic Day 21 (E21), Embryonic Day 27 (E27), Hatching Day (D0), and Post-hatching Day 7 (D7), were used to isolate total RNA for analysis.

RESULTS

A total of 68,161 genes and 472 mature microRNAs were identified. In order to uncover deeper insights into the regulation of mRNA by miRNAs, we conducted an integration of the differentially expressed miRNAs (known as DEMs) with the differentially expressed genes (referred to as DEGs) across various developmental stages. This integration allowed us to make predictions regarding the interactions between miRNAs and mRNA. Through this analysis, we identified a total of 274 DEGs that may serve as potential targets for the 68 DEMs. In the predicted miRNA‒mRNA interaction networks, let-7b, miR-133a-3p, miR-301a-3p, and miR-338-3p were the hub miRNAs. In addition, multiple DEMs also showed predicted target relationships with the DEGs associated with skeletal system development. These identified DEGs and DEMs as well as their predicted interaction networks involved in the regulation of energy homeostasis and muscle development were most likely to play critical roles in facilitating the embryo-to-hatchling transition. A candidate miRNA, miR-301a-3p, exhibited increased expression during the differentiation of satellite cells and was downregulated in the breast muscle tissues of Muscovy ducks at E21 compared to E27. A dual-luciferase reporter assay suggested that the ANKRD1 gene, which encodes a transcription factor, is a direct target of miR-301a-3p.

CONCLUSIONS

miR-301a-3p suppressed the posttranscriptional activity of ANKRD1, which is an activator of satellite cell proliferation, as determined with gain- and loss-of-function experiments. miR-301a-3p functions as an inducer of myogenesis by targeting the ANKRD1 gene in Muscovy ducks. These results provide novel insights into the early developmental process of black Muscovy breast muscles and will improve understanding of the underlying molecular mechanisms.

AAV-mediated expression of PFKFB3 in myofibers, but not endothelial cells, improves ischemic muscle function in mice with critical limb ischemia

6-Phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3) is a powerful driver of angiogenesis through its modulation of glycolytic metabolism within endothelial cells. Recent work has demonstrated that PFKFB3 modulates the response to muscle ischemia, however the cell specificity of these effects is not fully understood. In this study, we tested the impact of viral mediated expression of PFKFB3, driven by gene promoters specific for myofibers or endothelial cells, on ischemic hindlimb revascularization and muscle function. We hypothesized that both endothelium- and muscle-specific expression of PFKFB3 would attenuate limb pathology following femoral artery ligation. Male and female BALB/cJ mice were injected with adeno-associated virus encoding the either a green fluorescent protein (GFP) or PFKFB3 driven by either the human skeletal actin (ACTA1) or cadherin-5 (Cdh5) promoters. Four weeks after AAV treatment, mice were subjected to unilateral femoral artery ligation and limb perfusion and muscle function were assessed. Both endothelium- and muscle-specific PFKFB3 expression resulted in significantly more perfused capillaries within the ischemic limb muscle, but neither changed myofiber size/area. Muscle-, but not endothelium-specific, PFKFB3 expression significantly improved maximal force production in ischemic muscle (P=0.0005). Notably, there was a significant effect of sex on maximal force levels in both cohorts of mice (P=0.0075 and P=0.0481), indicating that female mice had higher ischemic muscle strength compared to male mice, regardless of treatment group. Taken together, these data demonstrate that while both muscle- and endothelium-specific expression of PFKFB3 enhanced ischemic revascularization, only muscle-specific PFKFB3 expression improved muscle function.

A New CT Analysis of Abdominal Wall after DIEP Flap Harvesting

The abdominal microsurgical flap based on the deep inferior epigastric artery perforator (DIEP) flap has become the most popular option worldwide for autologous breast reconstruction. Several authors have investigated the results of reconstructed breasts, but the literature lacks systematic reviews exploring the donor site of the abdominal wall. To fulfil our aims, a new diagnostic muscle imaging analysis was designed and implemented. This study focused on rectus abdominal muscle morphology and function in a single series of 12 consecutive patients analysed before and after breast reconstruction with a microsurgical DIEP flap. Patients were divided into two groups, namely, “ipsilateral reconstruction” and “contralateral reconstruction”, depending on the side of the flap harvest and breast reconstruction, then evaluated by computed tomography (CT) scans scheduled for tumor staging, and clinically examined by a physiatrist. Numerous alterations in muscle physiology were observed due to surgical dissection of perforator vessels, and rectus muscle distress without functional impairment was a common result. Postoperatively, patients undergoing “contralateral reconstruction” appeared to exhibit fewer rectus muscle alterations. Overall, only three patients were impacted by a long-term deterioration in their quality of life. On the basis of the newly developed and implemented diagnostic approach, we concluded that DIEP microsurgical breast reconstruction is a safe procedure without major complications at the donor site, even if long-term alterations of the rectus muscle are a common finding.

Circulating levels of inflammatory parameters pentraxin-3, cyclophilin and heparin-binding epidermal growth factor-like growth factor in patients with ST-elevation myocardial infarction

Inflammatory biomarkers - pentraxin-3 (PTX3), cyclophilin A (CypA) and heparin-binding epidermal growth factor-like growth factor (HB-EGF) were examined in patients with ST-segment elevation myocardial infarction (STEMI) undergoing revascularization with primary percutaneous coronary intervention (pPCI) and stent implanting. Investigated parameters were compared between patients with and without obstructive coronary artery disease (CAD). In addition, their changes were tested in circulation before and immediately after pPCI. The study group consisted of 81 STEMI patients. Patients were classified in the STEMI-CAD group if they had significant obstructive CAD or in MINOCA group if they had no significant stenosis. In STEMI-CAD patients inflammatory parameters were determined prior to and after pPCI intervention. Immediately after pPCI, in STEMI-CAD patients levels of PTX3 were significantly lower (1.52 vs. 2.17 μg/L, p < .001), while the levels of HB-EGF (14.61 vs. 12.03 pg/L, p < .001) and CyPA (15.95 vs. 8.62 μg/L, p < .001) were significantly higher compared to levels before pPCI. STEMI-CAD patients had lower PTX3 values 2.17 μg/L (1.55-5.10 μg/L) than MINOCA patients 5.06 μg/L (2.77-6.7 μg/L), p = .046. Diagnostic accuracy of PTX3 for discrimination MINOCA from STEMI-CAD patients was low (area under receiver operating characteristic curve = 0.770). Evaluation of PTX3 values may be helpful in the understanding of MINOCA aetiology but they couldn't distinguish stenosis severity in STEMI patients. Inflammatory biomarkers significantly changed after pPCI but the possibility of clinical use of these biomarkers needs to be evaluated in a larger prospective study.

Important signals regulating coronary artery angiogenesis

Angiogenesis is a complex process of budding, the formation of new blood vessels from pre-existing microvessels, via migration, proliferation and survival. Vascular angiogenesis factors include different classes of molecules that have a fundamental role in blood vessel formation. Numerous inducers of angiogenesis, such as the members of the vascular endothelial growth factor (VEGF) family, basic fibroblast growth factor (bFGF), angiopoietin (Ang), hepatocyte growth factor (HGF), and hypoxia inducible factor-1 (HIF-1), have an important role in angiogenesis. However, VEGF, platelet-derived growth factor (PDGF), and transforming growth factor β (TGF-β) expression appear to be important in intraplaque angiogenesis. Interaction and combined effects between growth factors is essential in endothelial cell migration, proliferation, differentiation, and endothelial cell-cell communication that ultimately lead to the microvessel formation. Since VEGF has a key role during angiogenesis; it may be considered as a good therapeutic target in the clinic. The essential function of several angiogenic factors involved in coronary angiogenesis and intraplaque angiogenesis in atherosclerosis are carefully considered along with the use of angiogenic factors in clinical practice.

PADPIN: protein-protein interaction networks of angiogenesis, arteriogenesis, and inflammation in peripheral arterial disease

Peripheral arterial disease (PAD) results from an obstruction of blood flow in the arteries other than the heart, most commonly the arteries that supply the legs. The complexity of the known signaling pathways involved in PAD, including various growth factor pathways and their cross talks, suggests that analyses of high-throughput experimental data could lead to a new level of understanding of the disease as well as novel and heretofore unanticipated potential targets. Such bioinformatic analyses have not been systematically performed for PAD. We constructed global protein-protein interaction networks of angiogenesis (Angiome), immune response (Immunome), and arteriogenesis (Arteriome) using our previously developed algorithm GeneHits. The term "PADPIN" refers to the angiome, immunome, and arteriome in PAD. Here we analyze four microarray gene expression datasets from ischemic and nonischemic gastrocnemius muscles at day 3 posthindlimb ischemia (HLI) in two genetically different C57BL/6 and BALB/c mouse strains that display differential susceptibility to HLI to identify potential targets and signaling pathways in angiogenesis, immune, and arteriogenesis networks. We hypothesize that identification of the differentially expressed genes in ischemic and nonischemic muscles between the strains that recovers better (C57BL/6) vs. the strain that recovers more poorly (BALB/c) will help for the prediction of target genes in PAD. Our bioinformatics analysis identified several genes that are differentially expressed between the two mouse strains with known functions in PAD including TLR4, THBS1, and PRKAA2 and several genes with unknown functions in PAD including EphA4, TSPAN7, SLC22A4, and EIF2a.

The epidermal growth factor receptor and its ligands in cardiovascular disease

The epidermal growth factor receptor (EGFR) family and its ligands serve as a switchboard for the regulation of multiple cellular processes. While it is clear that EGFR activity is essential for normal cardiac development, its function in the vasculature and its role in cardiovascular disease are only beginning to be elucidated. In the blood vessel, endothelial cells and smooth muscle cells are both a source and a target of EGF-like ligands. Activation of EGFR has been implicated in blood pressure regulation, endothelial dysfunction, neointimal hyperplasia, atherogenesis, and cardiac remodeling. Furthermore, increased circulating EGF-like ligands may mediate accelerated vascular disease associated with chronic inflammation. Although EGFR inhibitors are currently being used clinically for the treatment of cancer, additional studies are necessary to determine whether abrogation of EGFR signaling is a potential strategy for the treatment of cardiovascular disease.

Chronic inhibition of epidermal growth factor receptor tyrosine kinase and extracellular signal-regulated kinases 1 and 2 (ERK1/2) augments vascular response to limb ischemia in type 2 diabetic mice

Type 2 diabetes is a key risk factor for ischemia-dependent pathology; therefore, a significant medical need exists to develop novel therapies that increase the formation of new vessels. We explored the therapeutic potential of epidermal growth factor receptor tyrosine kinase (EGFRtk) and extracellular signal-regulated kinase 1/2 (ERK1/2) inhibition in impaired ischemia-induced neovascularization in type 2 diabetes. Unilateral femoral artery ligation was performed in diabetic (db(-)/db(-)) and their control (db(-)/db(+)) mice for 4 weeks, followed by treatments with EGFRtk and ERK1/2 inhibitors (AG1478, 10 mg/kg/day and U0126, 400 μg/kg/day, respectively) for 3 weeks. Neovascularization, blood flow recovery, vascular and capillary density, and endothelial nitric oxide synthase activity were significantly impaired and were associated with enhanced EGFRtk and ERK1/2 activity in db(-)/db(-) mice. EGFRtk and ERK1/2 inhibitors did not have any effect in control mice, while in db(-)/db(-) mice there was a significant increase in neovascularization, blood flow recovery, vascular and capillary density, endothelial nitric oxide synthase activity, and were associated with a decrease in EGFRtk and ERK1/2 activity. Our data demonstrated that the inhibition of EGFRtk and ERK1/2 restored ischemia-induced neovascularization and blood flow recovery in type 2 diabetic mice. Thus, EGFRtk and ERK1/2 could be possible targets to protect from ischemia-induced vascular pathology in type 2 diabetes.

Gene expression analysis of ischaemia and reperfusion in human microsurgical free muscle tissue transfer

The aim of this study was to analyse various gene expression profiles of muscle tissue during normoxia, ischaemia and after reperfusion in human muscle free flaps, to gain an understanding of the occurring regulatory, inflammatory and apoptotic processes on a cellular and molecular basis. Eleven Caucasian patients with soft tissue defects needing coverage with microsurgical free muscle flaps were included in this study. In all patients, the muscle samples were taken from free myocutaneous flaps. The first sample was taken before induction of ischaemia in normoxia (I), another one after ischaemia (II), and the last one was taken after reperfusion (III). The samples were analysed using DNA-microarray, real-time-quantitative-PCR and immunohistochemistry. DNA-microarray analysis detected multiple, differentially regulated genes when comparing the different groups (I–III) with statistical significance. Comparing ischaemia (II) versus normoxia (I) educed 13 genes and comparing reperfusion (III) versus ischaemia (II) educed 19 genes. The comparison of reperfusion (III) versus normoxia (I) yielded 100 differentially regulated genes. Real-time-quantitative-PCR confirmed the results of the DNA-microarrays for a subset of four genes (CASP8, IL8, PLAUR and S100A8). This study shows that ischaemia and reperfusion induces alterations on the gene expression level in human muscle free flaps. Data may suggest that the four genes CASP8, IL8, PLAUR and S100A8 are of great importance in this context. We could not confirm the DNA-microarry and real-time-quantitative-PCR results on the protein level. Finally, these findings correspond with the surgeon’s clinical experience that the accepted times of ischaemia, generally up to 90 min., are not sufficient to induce pathophysiological processes, which can ultimately lead to flap loss. When inflammatory and apoptotic proteins are expressed at high levels, flap damage might occur and flap loss is likely. The sole expression on mRNA level might explain why flap loss is unlikely.

Heparin-binding EGF-like growth factor promotes intestinal anastomotic healing

BACKGROUND

We have accumulated multiple lines of evidence supporting the ability of HB-EGF to protect the intestines from injury and to augment the healing of partial-thickness scald burns of the skin. The aim of the current study was to investigate the role of heparin-binding EGF-like growth factor (HB-EGF) in intestinal anastomotic wound healing.

MATERIALS AND METHODS

HB-EGF (-/-) knockout (KO) mice (n=42) and their HB-EGF (+/+) wild type (WT) counterparts (n=33), as well as HB-EGF transgenic (TG) mice (n=26) and their (WT) counterparts (n=27), underwent division and reanastomosis of the terminal ileum. In addition, WT mice (n=21) that received enteral HB-EGF (800 μg/kg) underwent the same operative procedure. Anastomotic bursting pressure was measured at 3 and 6 d postoperatively. Tissue sections were stained with hematoxylin and eosin to assess anastomotic healing, and Picrosirus red to assess collagen deposition. Immunohistochemistry using anti-von Willebrand factor antibodies was performed to assess angiogenesis. Complications and mortality were also recorded.

RESULTS

HB-EGF KO mice had significantly lower bursting pressures, lower healing scores, higher mortality, and higher complication rates postoperatively compared with WT mice. Collagen deposition and angiogenesis were significantly decreased in KO mice compared with WT mice. Conversely, HB-EGF TG mice had increased anastomotic bursting pressure, higher healing scores, lower mortality, lower complication rates, increased collagen deposition, and increased angiogenesis postoperatively compared with WT mice. WT mice that received HB-EGF had increased bursting pressures compared with non-HB-EGF treated mice.

CONCLUSION

Our results demonstrate that HB-EGF is an important factor involved in the healing of intestinal anastomoses.

Regions of arterial stenosis and clinical factors determining transcutaneous oxygen tension in patients with peripheral arterial disease

AIMS

Despite the clinical usefulness of transcutaneous oxygen tension (TcPO(2)) to assess the severity of limb ischemia, the factors determining TcPO(2) in patients with peripheral arterial disease (PAD) have not been fully clarified. We therefore examined the regions of arterial stenosis and clinical factors affecting lower-extremity TcPO(2).

METHODS

Resting TcPO(2) (REST-TcPO(2)) and postexercise TcPO(2) (Ex-TcPO(2)) in the calf region and the dorsalis pedis were measured simultaneously in 66 patients (132 limbs) with clinically suspected PAD, in whom angiography was also performed.

RESULTS

The peripheral arteries of the lower extremities were divided into five segments, and the impact of significant stenosis in each segment on ipsilateral TcPO(2) was evaluated by multiple regression analysis. In the calf region, significant stenosis of the proximal arteries (common-external iliac artery) revealed stronger involvement determining Ex-TcPO(2) than the peripheral segment (posterior tibial artery). In the dorsalis pedis, the peripheral segment (anterior tibial artery) more strongly determined Ex-TcPO(2) and REST-TcPO(2) than proximal segments. Age, creatinine, and diabetes were associated with REST-TcPO(2) of the calf region independent of arterial stenoses, while those of the dorsalis pedis were independently associated with age, and creatinine. In contrast, Ex-TcPO(2) in both regions was not independently associated with clinical factors, except for stenosis of the perfusing arteries.

CONCLUSION

The vascular lesions affecting TcPO(2) differ between the calf region (proximal > peripheral) and the dorsalis pedis (proximal < peripheral). In addition postexercise TcPO(2) is solely determined by stenosis of the perfusing arteries, while TcPO(2) at rest is affected by multiple clinical factors.

Acute vascular endothelial growth factor expression during hypertrophy is muscle phenotype specific and localizes as a striated pattern within fibres

Skeletal muscle hypertrophy requires the co-ordinated expression of locally acting growth factors that promote myofibre growth and concurrent adaptive changes in the microvasculature. These studies tested the hypothesis that vascular endothelial growth factor (VEGF) and heparin-binding epidermal growth factor (HB-EGF) expression are upregulated during the early stages of compensatory muscle growth induced by chronic functional overload (FO). Bilateral FO of the plantaris and soleus muscles was induced for 3 or 7 days in the hindlimbs of adult female Sprague-Dawley rats (n = 5 per group) and compared with control (non-FO) rats. Relative muscle mass (in mg (kg body weight)(-1)) increased by 18 and 24% after 3 days and by 20 and 33% after 7 days in the plantaris and soleus muscles, respectively. No differences in HB-EGF mRNA or protein were observed in either muscle of FO rats relative to control muscles. The VEGF mRNA was similar in the soleus muscles of FO and control rats, whereas a significant elevation occurred at 3 and 7 days of FO in the plantaris muscle. However, VEGF protein expression after 3 days of FO exhibited a differential response; expression in the soleus muscle decreased 1.6-fold, whereas that in the plantaris muscle increased 1.8-fold compared with the control muscle. After 7 days of FO, VEGF protein remained elevated within the plantaris muscle, but returned to basal levels in the soleus. Robust basal HB-EGF and VEGF protein expression was consistently seen in control muscles. In all groups, immunohistochemistry for VEGF protein displayed a distinct striated expression pattern within myofibres, with considerably less labelling in extracellular spaces. Constitutive expression of HB-EGF and VEGF in control myofibres is consistent with housekeeping roles for these growth factors in skeletal muscle tissue. However, the specific patterns of VEGF expression in these muscles during FO may reflect the chronic changes in neural recruitment between muscles and the co-ordination of angiogenic and/or other hypertrophic responses.

Modified multipotent stromal cells with epidermal growth factor restore vasculogenesis and blood flow in ischemic hind-limb of type II diabetic mice

Diabetes is increasing in the world and causes severe cardiovascular complications. Diabetes-induced limb ischemia leads to foot amputation and therapeutic remedies are urgently needed. Here we report that local injection of mesenchymal stem cells (MSCs) prestimulated with epidermal growth factor (EGF) restored blood flow and vasculogenesis in the ischemic hind-limb of type II diabetic (db(-)/db(-)) mice. Bone marrow cells from db(-)/db(-) mice are altered as evidenced by increased oxidative stress and reduced Akt and adhesion molecules when compared with control (db(-)/db(+)). Femoral artery ligation-induced ischemia was performed in the hind-limb of db(-)/db(-) and db(-)/db(+) mice for 28 days. Enhanced green fluorescent protein (EGFP)-MSCs stimulated+/-exogenous EGF for 24 h were injected locally into the ischemic muscle. Blood flow measured with MoorLDI-Laser and microangiography assessed with X-ray showed 100% recovery in db(-)/db(+) compared to 50% recovery in db(-)/db(-) mice. Interestingly, db(-)/db(-) mice had 60 and 96% blood flow recovery and 61 and 98% of vasculogenesis when treated with MSCs alone or MSCs modified with EGF, respectively. Western blot analysis of hind-limb muscles revealed an increase in Akt and vascular endothelial growth factor receptor phosphorylation and hypoxia-inducible factor) expression in db(-)/db(-) mice injected with MSCs or MSCs+EGF compared to db(-)/db(-) mice. Fluorescent microscopic images show that EGFP-MSCs differentiate into new microvessels. Adhesion and migration of MSCs on cultured endothelial cells were ICAM1-, VCAM1- and Akt-dependent mechanism and elevated when MSCs were prestimulated with EGF compared with nonstimulated MSCs. Our novel study data provide evidence that in type II diabetes, stimulated MSCs with EGF enhance the recovery of blood flow and angiogenesis.

Endothelial nitric oxide synthase deficiency causes collateral vessel rarefaction and impairs activation of a cell cycle gene network during arteriogenesis

RATIONALE

The collateral circulation is tissue- and life-saving in obstructive arterial disease. Disappointing outcomes in clinical trials aimed at augmenting collateral growth highlight the need for greater understanding of collateral biology.

OBJECTIVE

The role of endothelial nitric oxide synthase (eNOS) in forming native (preexisting) collaterals and remodeling in obstructive disease are unknown or controversial issues, respectively.

METHODS AND RESULTS

We compared the native collateral circulation in healthy tissue and collateral remodeling after femoral artery ligation (FAL) in wild-type and eNOS-knockout (KO) mice. Perfusion after FAL fell further in adult eNOS-KOs, in association with fewer native collaterals in hindlimb (confirmed in brain). This was not attributable to impaired collateral formation in the embryo-neonate, but rather from collateral loss during growth to adulthood. Compared to wild-type, eNOS-KOs evidenced reduced collateral remodeling, angiogenesis, and flow-mediated dilation of the arterial bed supplying the collaterals, resulting in lower perfusion and greater ischemic injury at all time points over 21 days following FAL. To probe the mechanism for impaired remodeling, we performed genome-wide expression profiling of isolated, remodeling hindlimb collaterals 24 hour after FAL. Upregulation of genes encoding cytokines/chemokines, inflammatory, stress response, and cell cycle proteins was evident in wild-type mice. In contrast, expression was lower in 40 of 44 cell cycle genes in eNOS-KO mice, in association with impaired proliferation of vascular wall cells.

CONCLUSIONS

Our findings suggest a novel role for eNOS in maintaining native collateral density during natural growth to adulthood and in collateral remodeling in obstructive disease, the latter through regulation of cell proliferation.

Deletion of the heparin-binding epidermal growth factor-like growth factor gene increases susceptibility to necrotizing enterocolitis

BACKGROUND

Necrotizing enterocolitis (NEC) is the leading surgical cause of death in premature infants. We have accumulated evidence supporting a role for heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF) in protection of the intestines from NEC. The aim of the current study was to evaluate the effect of loss-of-function of endogenous HB-EGF on susceptibility to NEC.

METHODS

Neonatal HB-EGF((-/-)) knockout (KO) mice and their HB-EGF((+/+)) wild-type (WT) counterparts were exposed to experimental NEC. An additional group of HB-EGF KO pups were also exposed to NEC but had HB-EGF added to their formula. To examine gut barrier function, HB-EGF KO and WT pups received intragastric fluorescein isothiocyanate-labeled dextran (FITC dextran) under basal and stressed conditions, and serum FITC dextran levels were measured.

RESULTS

The WT mice had an incidence of NEC of 53%, whereas HB-EGF KO mice had a significantly increased incidence of NEC of 80% (P = .04). Importantly, administration of exogenous HB-EGF to HB-EGF KO pups significantly reduced the incidence of NEC to 45% (P = .04). Heparin-binding EGF KO mice had significantly increased intestinal permeability compared to WT mice under basal and stressed conditions.

CONCLUSIONS

Our results provide evidence that loss of the HB-EGF gene increases susceptibility to NEC and that administration of exogenous HB-EGF reverses this susceptibility.

Marvels, mysteries, and misconceptions of vascular compensation to peripheral artery occlusion

Peripheral arterial disease is a major health problem and there is a significant need to develop therapies to prevent its progression to claudication and critical limb ischemia. Promising results in rodent models of arterial occlusion have generally failed to predict clinical success and led to questions of their relevance. While sub-optimal models may have contributed to the lack of progress, we suggest that advancement has also been hindered by misconceptions of the human capacity for compensation and the specific vessels which are of primary importance. We present and summarize new and existing data from humans, Ossabaw miniature pigs, and rodents which provide compelling evidence that natural compensation to occlusion of a major artery (i) may completely restore perfusion, (ii) occurs in specific pre-existing small arteries, rather than the distal vasculature, via mechanisms involving flow-mediated dilation and remodeling (iii) is impaired by cardiovascular risk factors which suppress the flow-mediated mechanisms and (iv) can be restored by reversal of endothelial dysfunction. We propose that restoration of the capacity for flow-mediated dilation and remodeling in small arteries represents a largely unexplored potential therapeutic opportunity to enhance compensation for major arterial occlusion and prevent the progression to critical limb ischemia in the peripheral circulation.

Redox-dependent mechanisms in coronary collateral growth: the "redox window" hypothesis

This review addresses the complexity of coronary collateral growth from the aspect of redox signaling and introduces the concept of a "redox window" in the context of collateral growth. In essence, the redox window constitutes a range in the redox state of cells, which not only is permissive for the actions of growth factors but also amplifies their actions. The interactions of redox-dependent signaling with growth factors are well established through the actions of many redox-dependent kinases (e.g., Akt and p38 mitogen-activated protein kinase). The initial changes in cellular redox can be induced by a variety of events, from the oxidative burst during reperfusion after ischemia, to recruitment of various types of inflammatory cells capable of producing reactive oxygen species. Any event that "upsets" the normal redox equilibrium is capable of amplifying growth. However, extremes of the redox window, oxidative and reductive stresses, are associated with diminished growth-factor signaling and reduced activation of redox-dependent kinases. This concept of a redox window helps to explain why the clinical trials aimed at stimulating coronary collateral growth, the "therapeutic angiogenesis trials," failed. However, understanding of redox signaling in the context of coronary collateral growth could provide new paradigms for stimulating collateral growth in patients.

Amplification of coronary arteriogenic capacity of multipotent stromal cells by epidermal growth factor

OBJECTIVE

We determined whether increasing adherence of multipotent stromal cells (MSCs) would amplify their effects on coronary collateral growth (CCG).

METHODS AND RESULTS

Adhesion was established in cultured coronary endothelials cells (CECs) or MSCs treated with epidermal growth factor (EGF). EGF increased MSCs adhesion to CECs, and increased intercellular adhesion molecule (ICAM-1) or vascular cell adhesion molecule (VCAM-1) expression. Increased adherence was blocked by EGF receptor antagonism or antibodies to the adhesion molecules. To determine whether adherent MSCs, treated with EGF, would augment CCG, repetitive episodes of myocardial ischemia (RI) were introduced and CCG was measured from the ratio of collateral-dependent (CZ) and normal zone (NZ) flows. CZ/NZ was increased by MSCs without treatment versus RI-control and was further increased by EGF-treated MSCs. EGF-treated MSCs significantly improved myocardial function versus RI or RI+MSCs demonstrating that the increase in collateral flow was functionally significant. Engraftment of MSCs into myocardium was also increased by EGF treatment.

CONCLUSIONS

These results reveal the importance of EGF in MSCs adhesion to endothelium and suggest that MSCs may be effective therapies for the stimulation of coronary collateral growth when interventions are used to increase their adhesion and homing (in vitro EGF treatment) to the jeopardized myocardium.

Suppressed hindlimb perfusion in Rac2-/- and Nox2-/- mice does not result from impaired collateral growth

While tissue perfusion and angiogenesis subsequent to acute femoral artery occlusion are suppressed in NADPH oxidase 2 (Nox2)-null (Nox2(-/-)) mice, studies have not established the role of Nox2 in collateral artery enlargement. Rac2 is a small GTPase that binds Nox2 and activates Nox2-based NAD(P)H oxidase but, unlike Nox2, is primarily restricted to bone marrow-derived cells. In this study, we used Rac2-null (Rac2(-/-)) and Nox2(-/-) mice with a novel method of identifying primary hindlimb collaterals to investigate the hypothesis that collateral growth requires these molecules. When initial experiments performed with femoral ligation demonstrated similar perfusion and collateral growth in Rac2(-/-) and wild-type C57BL/6J (BL6) mice, subsequent experiments were performed with a more severe ischemia model, femoral artery excision. After femoral excision, tissue perfusion was suppressed in Rac2(-/-) mice relative to BL6 mice. Histological assessment of ischemic injury including necrotic and regenerated muscle fibers and lipid and collagen deposition demonstrated greater injury in Rac2(-/-) mice. The diameters of primary collaterals identified during Microfil injection with intravital microscopy were enlarged to a similar extent in BL6 and Rac2(-/-) mice. Intimal cells in collateral cross sections were increased in number in both strains and were CD31 positive and CD45 negative. Circulating leukocytes and CD11b(+) cells were increased more in Rac2(-/-) than BL6 animals. Experiments performed in Nox2(-/-) mice to verify that the unexpected results related to collateral growth were not unique to Rac2(-/-) mice gave equivalent results. The data demonstrate that, subsequent to acute femoral artery excision, perfusion recovery is impaired in Rac2(-/-) and Nox2(-/-) mice but that collateral luminal expansion and intimal cell recruitment/proliferation are normal. These novel results indicate that collateral luminal expansion and intimal cell recruitment/proliferation are not mediated by Rac2 and Nox2.

Heparin-binding epidermal growth factor-like growth factor gene disruption is associated with delayed intestinal restitution, impaired angiogenesis, and poor survival after intestinal ischemia in mice

PURPOSE

We have demonstrated that administration of heparin-binding epidermal growth factor-like growth factor (HB-EGF) protects the intestines from injury. The aim of the current study was to evaluate the effect of HB-EGF gene disruption on intestinal restitution, angiogenesis, and long-term survival after intestinal ischemia/reperfusion (I/R) injury.

METHODS

HB-EGF (-/-) and wild-type HB-EGF (+/+) littermate mice were subjected to 45 minutes of superior mesenteric artery occlusion followed by reperfusion. Functional recovery of the gut permeability barrier was evaluated with Ussing chamber studies, and microvessel density was evaluated immunohistochemically. Animal survival was evaluated using the Kaplan-Meier method.

RESULTS

Histologic damage after ischemia was significantly higher in HB-EGF (-/-) mice compared with HB-EGF (+/+) mice, associated with a significantly higher number of incompetent (nonhealed, nonresurfaced) villi indicative of delayed structural healing by restitution. HB-EGF (-/-) mice had increased intestinal permeability after intestinal I/R. HB-EGF (-/-) mice had significantly lower microvessel density at 3 and 7 days after I/R, indicating that HB-EGF gene deletion resulted in delayed onset of angiogenesis. Two-week mortality rates were significantly higher in HB-EGF (-/-) mice.

CONCLUSIONS

Endogenous HB-EGF significantly enhances healing by restitution, prolongs survival, and enhances angiogenesis in mice subjected to intestinal I/R injury. These findings support our hypothesis that HB-EGF administration may improve outcome in patients with intestinal I/R injury, including necrotizing enterocolitis.

Heparin-binding epidermal growth factor-like growth factor signaling in flow-induced arterial remodeling

Heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF) is activated by reduced endothelial shear stress and stimulates smooth muscle cell proliferation in vitro. Moreover, HB-EGF is augmented at sites of intimal hyperplasia and atherosclerosis, conditions favored by low/disturbed shear stress. We thus tested whether HB-EGF contributes to low flow-induced negative hypertrophic remodeling (FINR) of a mouse carotid artery. Blood flow was surgically decreased in the left and increased in the right common carotid arteries. After 21 days, the left carotid artery exhibited lumen narrowing, thickening of intima-media and adventitia, and increased circumference that were inhibited by approximately 50% in HB-EGF(+/-) and approximately 90% in HB-EGF(-/-) mice. FINR was also inhibited by the EGF receptor inhibitor AG1478. In contrast, eutrophic outward remodeling of the right carotid artery was unaffected in HB-EGF(+/-) and HB-EGF(-/-) mice, nor by AG1478. FINR-induced proliferation and leukocyte accumulation were reduced in HB-EGF(-/-). FINR was associated with increased reactive oxygen species, increased expression of pro-HB-EGF and tumor necrosis factor alpha-converting enzyme (pro-HB-EGF sheddase), increased phosphorylation of EGF receptor and extracellular signal-regulated kinase 1/2, and increased nuclear factor kappaB activity. Apocynin and deletion of p47(phox) inhibited FINR, whereas deletion of HB-EGF abolished nuclear factor kappaB activation in smooth muscle cells. These findings suggest that HB-EGF signaling is required for low flow-induced hypertrophic remodeling and may participate in vascular wall disease and remodeling.

Collateral density, remodeling, and VEGF-A expression differ widely between mouse strains

Substantial variability exists in collateral density and ischemia-induced collateral growth among species. To begin to probe the underlying mechanisms, which are unknown, we characterized two mouse strains with marked differences in both parameters. Immediately after femoral artery ligation, collateral and foot perfusion were lower in BALB/c than C57BL/6 (P < 0.05 here and below), suggesting fewer pre-existing collaterals. This was confirmed with angiography and immunohistochemistry (approximately 35% fewer collaterals in the BALB/c's thigh). Recovery of hindlimb perfusion was attenuated in BALB/c, in association with 54% less collateral remodeling, reduced angiogenesis, greater ischemia, and more impaired hindlimb use. Densities of CD45+ and CD4+ leukocytes around collaterals increased similarly, but TNF-alpha expression was 50% lower in BALB/c, which may contribute to reduced collateral remodeling. In normal tissues, compared with C57BL/6, BALB/c exhibit an altered arterial branching pattern and, like skeletal muscle above, have 30% fewer collaterals in intestine and, remarkably, almost none in pial circulation, resulting in greatly impaired perfusion after cerebral artery occlusion. Ischemic induction of VEGF-A was attenuated in BALB/c. Analysis of a C57BL/6 x BALB/c recombinant inbred strain dataset identified a quantitative trait locus for VEGF-A mRNA abundance at or near the Vegfa locus that associates with lower expression in BALB/c. This suggests a cis-acting polymorphism in the Vegfa gene in BALB/c could contribute to reduced VEGF-A expression and, in turn, the above deficiencies in this strain. These findings suggest these strains offer a model to investigate genetic determinants of collateral formation and growth in ischemia.

Role of adenosine receptors in the regulation of angiogenic factors and neovascularization in hypoxia

Because hypoxia increases extracellular adenosine levels and stimulates angiogenesis, we evaluated the relative roles of reduced oxygen concentrations and adenosine receptor activation in the production of angiogenic factors. In vitro, we analyzed the effects of hypoxia and adenosine on the secretion of angiogenic factors from human microvascular endothelial cells (HMEC-1). To study the effects of hypoxia alone, we scavenged adenosine from the hypoxic medium with adenosine deaminase, and we used the stable adenosine analog 5'-N-ethylcarboxamidoadenosine (NECA) to study the effects of stimulation of adenosine receptors. In the absence of adenosine, hypoxia stimulated vascular endothelial growth factor (VEGF) but not interleukin-8 (IL-8) secretion from HMEC-1. In contrast, NECA stimulated both VEGF and IL-8 secretion. VEGF secretion was increased 1.9 +/- 0.04-fold with NECA (10 microM) and 1.7 +/- 0.1-fold with hypoxia (5% O(2)) but 3.8 +/- 0.1-fold when these two stimuli were combined. Thus, adenosine receptors act in a cooperative fashion with hypoxia to stimulate VEGF and induce IL-8 secretion not stimulated by hypoxia alone. In vivo, antagonism of adenosine receptors with caffeine abrogated VEGF up-regulation induced by local injection of NECA into the mouse hind limb and produced a 46% reduction of neovascularization in a mouse ischemic hind limb model. Our study suggests that adenosine actions are not redundant but rather are complementary to the direct effects of hypoxia. Stimulation of adenosine receptors not only contributes to the overall effect of hypoxia but also has additional actions in the regulation of angiogenic factors. Thus, adenosine receptors represent a potential therapeutic target for regulation of neovascularization.