Genetic deletion of TNFR2 augments inflammatory response and blunts satellite-cell-mediated recovery response in a hind limb ischemia model.

We have previously shown that TNF-tumor necrosis factor receptor-2/p75 (TNFR2/p75) signaling plays a critical role in ischemia-induced neovascularization in skeletal muscle and heart tissues. To determine the role of TNF-TNFR2/p75 signaling in ischemia-induced inflammation and muscle regeneration, we subjected wild-type (WT) and TNFR2/p75 knockout (p75KO) mice to hind limb ischemia (HLI) surgery. Ischemia induced significant and long-lasting inflammation associated with considerable decrease in satellite-cell activation in p75KO muscle tissue up to 10 d after HLI surgery. To determine the possible additive negative roles of tissue aging and the absence of TNFR2/p75, either in the tissue or in the bone marrow (BM), we generated 2 chimeric BM transplantation (BMT) models where both young green fluorescent protein (GFP)-positive p75KO and WT BM-derived cells were transplanted into adult p75KO mice. HLI surgery was performed 1 mo after BMT, after confirming complete engraftment of the recipient BM with GFP donor cells. In adult p75KO with the WT-BMT, proliferative (Ki67(+)) cells were detected only by d 28 and were exclusively GFP(+), suggesting significantly delayed contribution of young WT-BM cell to adult p75KO ischemic tissue recovery. No GFP(+) young p75KO BM cells survived in adult p75KO tissue, signifying the additive negative roles of tissue aging combined with decreased/absent TNFR2/p75 signaling in postischemic recovery.

Glutathione adducts on sarcoplasmic/endoplasmic reticulum Ca2+ ATPase Cys-674 regulate endothelial cell calcium stores and angiogenic function as well as promote ischemic blood flow recovery.

The sarco/endoplasmic reticulum Ca(2+) ATPase (SERCA) is key to Ca(2+) homeostasis and is redox-regulated by reversible glutathione (GSH) adducts on the cysteine (C) 674 thiol that stimulate Ca(2+) uptake activity and endothelial cell angiogenic responses in vitro. We found that mouse hind limb muscle ischemia induced S-glutathione adducts on SERCA in both whole muscle tissue and endothelial cells. To determine the role of S-glutathiolation, we used a SERCA 2 C674S heterozygote knock-in (SKI) mouse lacking half the key thiol. Following hind limb ischemia, SKI animals had decreased SERCA S-glutathione adducts and impaired blood flow recovery. We studied SKI microvascular endothelial cells in which total SERCA 2 expression was unchanged. Cultured SKI microvascular endothelial cells showed impaired migration and network formation compared with wild type (WT). Ca(2+) studies showed decreased nitric oxide (·NO)-induced (45)Ca(2+) uptake into the endoplasmic reticulum (ER) of SKI cells, while Fura-2 studies revealed lower Ca(2+) stores and decreased vascular endothelial growth factor (VEGF)- and ·NO-induced Ca(2+) influx. Adenoviral overexpression of calreticulin, an ER Ca(2+) binding protein, increased ionomycin-releasable stores, VEGF-induced Ca(2+) influx and endothelial cell migration. Taken together, these data indicate that the redox-sensitive Cys-674 thiol on SERCA 2 is required for normal endothelial cell Ca(2+) homeostasis and ischemia-induced angiogenic responses, revealing a novel redox control of angiogenesis via Ca(2+) stores.

Divergent roles for adiponectin receptor 1 (AdipoR1) and AdipoR2 in mediating revascularization and metabolic dysfunction in vivo.

Adiponectin is a well described anti-inflammatory adipokine that is highly abundant in serum. Previous reports have found that adiponectin deficiency promotes cardiovascular and metabolic dysfunction in murine models, whereas its overexpression is protective. Two candidate adiponectin receptors, AdipoR1 and AdipoR2, are uncharacterized with regard to cardiovascular tissue homeostasis, and their in vivo metabolic functions remain controversial. Here we subjected AdipoR1- and AdipoR2-deficient mice to chronic hind limb ischemic surgery. Blood flow recovery in AdipoR1-deficient mice was similar to wild-type; however, revascularization in AdipoR2-deficient mice was severely attenuated. Treatment with adiponectin enhanced the recovery of wild-type mice but failed to rescue the impairment observed in AdipoR2-deficient mice. In view of this divergent receptor function in the hind limb ischemia model, AdipoR1- and AdipoR2-deficient mice were also evaluated in a model of diet-induced obesity. Strikingly, AdipoR1-deficient mice developed severe metabolic dysfunction compared with wild type, whereas AdipoR2-deficient mice were protected from diet-induced weight gain and metabolic perturbations. These data show that AdipoR2, but not AdipoR1, is functionally important in an in vivo model of ischemia-induced revascularization and that its expression is essential for the revascularization actions of adiponectin. These data also show that, in contrast to revascularization responses, AdipoR1, but not AdipoR2 deficiency, leads to diet-induced metabolic dysfunction, revealing that these receptors have highly divergent roles in vascular and metabolic homeostasis.

Sonic hedgehog therapy in a mouse model of age-associated impairment of skeletal muscle regeneration.

Sonic hedgehog (Shh) is a morphogen regulating muscle development during embryogenesis. We have shown that the Shh pathway is postnatally recapitulated after injury and during regeneration of the adult skeletal muscle and regulates angiogenesis and myogenesis after muscle injury. Here, we demonstrate that in 18-month-old mice, there is a significant impairment of the upregulation of the Shh pathway that physiologically occurs in the young skeletal muscle after injury. Such impairment is even more pronounced in 24-month-old mice. In old animals, intramuscular therapy with a plasmid encoding the human Shh gene increases the regenerative capacities of the injured muscle, in terms of Myf5-positive cells, regenerating myofibers, and fibrosis. At the molecular level, Shh treatment increases the upregulation of the prototypical growth factors, insulin-like growth factor-1 and vascular endothelial growth factor. These data demonstrate that Shh increases regeneration after injury in the muscle of 24-month-old mice and suggest that the manipulation of the Shh pathway may be useful for the treatment of muscular diseases associated with aging.

Angiogenic impairment of the vascular endothelium: a novel mechanism and potential therapeutic target in muscular dystrophy.

OBJECTIVE: Dystrophin, the missing or defective protein in Duchenne muscular dystrophy, is expressed not only in muscle cells but also in vascular endothelial cells (ECs). In this study, we assessed the effects of dystrophin deficiency on the angiogenic capacities of ECs. APPROACH AND RESULTS: We isolated vascular ECs from mdx mice, the murine equivalent of Duchenne muscular dystrophy in humans, and wild-type controls, and we found that mdx-derived ECs have impaired angiogenic properties, in terms of migration, proliferation, and tube formation. They also undergo increased apoptosis in vitro compared with wild-type cells and have increased senescence-associated ß-galactosidase activity. Mdx-derived ECs also display reduced ability to support myoblast proliferation when cocultured with satellite cell-derived primary myoblasts. These endothelial defects are mirrored by systemic impairment of angiogenesis in vivo, both on induction of ischemia, stimulation with growth factors in the corneal model and matrigel plug assays, and tumor growth. We also found that dystrophin forms a complex with endothelial NO synthase and caveolin-1 in ECs, and that NO production and cGMP formation are compromised in ECs isolated from mdx mice. Interestingly, treatment with aspirin enhances production of both cGMP and NO in dystrophic ECs, whereas low-dose aspirin improves the dystrophic phenotype of mdx mice in vivo, in terms of resistance to physical exercise, muscle fiber permeability, and capillary density. CONCLUSIONS: These findings demonstrate that impaired angiogenesis is a novel player and potential therapeutic target in Duchenne muscular dystrophy.

T-cadherin is essential for adiponectin-mediated revascularization.

Adipose tissue secretes protein factors that have systemic actions on cardiovascular tissues. Previous studies have shown that ablation of the adipocyte-secreted protein adiponectin leads to endothelial dysfunction, whereas its overexpression promotes wound healing. However, the receptor(s) mediating the protective effects of adiponectin on the vasculature is not known. Here we examined the role of membrane protein T-cadherin, which localizes adiponectin to the vascular endothelium, in the revascularization response to chronic ischemia. T-cadherin-deficient mice were analyzed in a model of hind limb ischemia where blood flow is surgically disrupted in one limb and recovery is monitored over 28 days by laser Doppler perfusion imaging. In this model, T-cadherin-deficient mice phenocopy adiponectin-deficient mice such that both strains display an impaired blood flow recovery compared with wild-type controls. Delivery of exogenous adiponectin rescued the impaired revascularization phenotype in adiponectin-deficient mice but not in T-cadherin-deficient mice. In cultured endothelial cells, T-cadherin deficiency by siRNA knockdown prevented the ability of adiponectin to promote cellular migration and proliferation. These data highlight a previously unrecognized role for T-cadherin in limb revascularization and show that it is essential for mediating the vascular actions of adiponectin.

Endothelial dysfunction and systemic hypertension by selective cGMP-dependent protein kinase I inhibition using novel cell-penetrating peptide delivered in vivo.

BACKGROUND AND OBJECTIVE: Nitric oxide (NO) and related nitrovasodilators regulate blood pressure by activation of soluble guanylate cyclase, elevation of cyclic guanosine monophosphate (cGMP), and activation of cGMP-dependent protein kinase (cGPK). Despite the progress of our understanding of the NO/cGMP mediated vasorelaxation, partly through conventional cGPK knock-out mice, the role of cGPK remains unclear. In particular, the downstream target(s) of the kinase are not well defined. We hypothesized that highly selective inhibitors of cGPK delivered in vivo in adult may elucidate the role of the kinase in vasorelaxation and regulation of blood pressure. METHODS AND RESULTS: We have adopted a newly developed method of TAT-mediated protein transduction to study NO/cGMP signaling pathways in mice. In vitro, TAT-cGPK inhibitor peptide blocked autophosphorylation of the kinase. The effect of cGPK inhibition on murine blood pressure (BP) was investigated by continuous infusion of 100 µg of the inhibitor into the internal jugular vein over 72 hours. In 8 animals infused with the inhibitor, the mean BP increased by 38 ± 24/31 ± 30 mm Hg (from 108 ± 14/92 ± 19 to 145 ± 13/123 ± 19 mm Hg) whereas in 8 animals injected with either saline (4) or TAT-green fluorescent protein (4), the BP remained the same (from 117 ± 21/101 ± 26 to 119 ± 22/96 ± 30 mm Hg); P=0.001. Ex vivo, using vascular ring assays, NO-dependent relaxation in murine aortas harvested from animals administered with TAT-cGPK inhibitor was inhibited by 25% (sham 76 ± 11%, inhibitor 51 ± 13%). CONCLUSION: We demonstrated that highly specific peptide inhibitor of cGPK induced adult murine hypertension through inhibition of nitric oxide mediated relaxation.

Pleiotropic beneficial effects of sonic hedgehog gene therapy in an experimental model of peripheral limb ischemia.

We have previously shown that the signaling pathway of the embryonic morphogen Sonic hedgehog (Shh) is recapitulated in the postnatal skeletal muscle in response to ischemia. We have also demonstrated that Shh is an indirect angiogenic agent upregulating various families of angiogenic growth factors and that Shh gene therapy improves angiogenesis and heart function in experimental models of myocardial ischemia. Based on these findings, we hypothesized that Shh gene therapy is beneficial in an experimental model of peripheral ischemia. We found that intramuscular (i.m.) treatment with a plasmid encoding the Shh human gene (phShh) increased blood flow, capillary density, and arteriole density in mice in which peripheral circulation of the hindlimb was disrupted by removal of the common femoral artery. Shh gene therapy also enhanced vasculogenesis, by increasing the number of circulating bone marrow (BM)-derived endothelial precursors and improving the contribution of these cells to the process of neovascularization. Finally, phShh treatment induced upregulation of prototypical angiogenic, arteriogenic, and vasculogenic factors, such as vascular endothelial growth factor (VEGF), angiopoietin 1 (Ang-1), and stromal cell-derived factor-1 (SDF-1α). These data suggest that Shh gene therapy merits further investigation for its ability to trigger the expression of potent trophic factors and stimulate pleiotropic aspects of neovascularization in the setting of ischemia.

Autologous transplantation of endothelial progenitor cells genetically modified by adeno-associated viral vector delivering insulin-like growth factor-1 gene after myocardial infarction.

The regenerative potential of bone marrow-derived endothelial progenitor cells (EPCs) has been adapted for the treatment of myocardial and limb ischemia via ex vivo expansion. We sought to enhance EPC function by the efficient genetic modification of EPCs in a rat model of myocardial infarction. Peripheral blood EPCs were expanded and transduced, using adeno-associated virus (AAV). AAV-mediated EPC transduction efficacy was 23 ± 1.2%, which was improved by 4.0- to 7.2-fold after pretreatment with the tyrosine kinase inhibitor genistein. Adult rats (n = 7 in each group) underwent myocardial infarction by left anterior descending coronary artery occlusion, and received autologous EPCs transduced by AAV-IGF-1 or AAV-lacZ into the periinfarct area. Echocardiography demonstrated that cardiac function in the IGF-1-EPC group was significantly improved compared with the lacZ-EPC control group 12 weeks after myocardial infarction. In addition, IGF-1-expressing EPCs led to reduced cardiac apoptosis, increased cardiomyocyte proliferation, and increased numbers of capillaries in the periinfarct area. AAV expression was limited to the targeted heart region only. Pretreatment with genistein markedly improved AAV transduction of EPCs. IGF-1-expressing EPCs exhibit favorable cell-protective effects with tissue-limited expression in rat heart postinfarction.

Neuregulin-1 attenuated doxorubicin-induced decrease in cardiac troponins.

Neuregulin-1 (NRG1) is a potential therapeutic agent for the treatment of doxorubicin (Dox)-induced heart failure. NRG1, however, activates the erbB2 receptor, which is frequently overexpressed in breast cancers. It is, therefore, important to understand how NRG1, via erbB2, protects the heart against Dox cardiotoxicity. Here, we studied NRG1-erbB2 signaling in Dox-treated mice hearts and in isolated neonatal rat ventricular myocytes (NRVM). Male C57BL/6 mice were treated with recombinant NRG1 before and daily after a single dose of Dox. Cardiac function was determined by catheterization. Two-week survival was analyzed by the Kaplan-Meier method. Cardiac troponins [cardiac troponin I (cTnI) and cardiac troponin T (cTnT)] and phosphorylated Akt protein levels were determined in mice hearts and in NRVM by Western blot analysis. Activation of caspases and ubiquitinylation of troponins were determined in NRVM by caspase assay and immunoprecipitation. NRG1 significantly improved survival and cardiac function in Dox-treated mice. NRG1 reduced the decrease in cTnI, cTnT, and cardiac troponin C (cTnC) and maintained Akt phosphorylation in Dox-treated mice hearts. NRG1 reduced the decrease in cTnI and cTnT mRNA and proteins in Dox-treated NRVM. Inhibition of erbB2, phosphoinositide 3-kinase (PI3K), Akt, and mTOR blocked the protective effects of NRG1 on cTnI and cTnT in NRVM. NRG1 significantly reduced Dox-induced caspase activation, which degraded troponins, in NRVM. NRG1 reduced Dox-induced proteasome degradation of cTnI. NRG1 attenuates Dox-induced decrease in cardiac troponins by increasing transcription and translation and by inhibiting caspase activation and proteasome degradation of troponin proteins. NRG1 maintains cardiac troponins by the erbB2-PI3K pathway, which may lessen Dox-induced cardiac dysfunction.

Dual angiogenic and neurotrophic effects of bone marrow-derived endothelial progenitor cells on diabetic neuropathy.

BACKGROUND: Endothelial progenitor cells (EPCs) are known to promote neovascularization in ischemic diseases. Recent evidence suggested that diabetic neuropathy is causally related to impaired angiogenesis and deficient growth factors. Accordingly, we investigated whether diabetic neuropathy could be reversed by local transplantation of EPCs. METHODS AND RESULTS: We found that motor and sensory nerve conduction velocities, blood flow, and capillary density were reduced in sciatic nerves of streptozotocin-induced diabetic mice but recovered to normal levels after hind-limb injection of bone marrow-derived EPCs. Injected EPCs were preferentially and durably engrafted in the sciatic nerves. A portion of engrafted EPCs were uniquely localized in close proximity to vasa nervorum, and a smaller portion of these EPCs were colocalized with endothelial cells. Multiple angiogenic and neurotrophic factors were significantly increased in the EPC-injected nerves. These dual angiogenic and neurotrophic effects of EPCs were confirmed by higher proliferation of Schwann cells and endothelial cells cultured in EPC-conditioned media. CONCLUSIONS: We demonstrate for the first time that bone marrow-derived EPCs could reverse various manifestations of diabetic neuropathy. These therapeutic effects were mediated by direct augmentation of neovascularization in peripheral nerves through long-term and preferential engraftment of EPCs in nerves and particularly vasa nervorum and their paracrine effects. These findings suggest that EPC transplantation could represent an innovative therapeutic option for treating diabetic neuropathy.

Estradiol-induced, endothelial progenitor cell-mediated neovascularization in male mice with hind-limb ischemia.

We investigated whether administration of estradiol to male mice augments mobilization of bone marrow-derived endothelial progenitor cells (EPC) and incorporation into foci of neovascularization after hind-limb ischemia, thereby contributing to blood flow restoration. Mice were randomized and implanted with placebo pellets or pellets containing low-dose estradiol (0.39 mg) or high-dose estradiol (1.7 mg). Hind-limb ischemia was induced by unilateral resection of the left femoral artery 1 week after pellet implantation, then EPC mobilization and functional recovery was evaluated. EPC recruitment was assessed in mice transplanted with bone marrow from transgenic donors expressing beta-galactosidase driven by the Tie-2 promoter. EPC culture assay performed 2 weeks after pellet implantation revealed a significantly greater (p<0.05) number of circulating EPCs in the high-dose estradiol group than in the low-dose estradiol and placebo groups. At 3 and 4 weeks after induction of hind-limb ischemia, perfusion was significantly greater (p<0.05) in high-dose estradiol mice than in mice implanted with the low-dose estradiol or placebo pellets. At 1 and 4 weeks after hind-limb ischemia surgery, more bone marrow-derived EPCs, identified as beta-galactosidase-positive cells, were observed in ischemic regions from high-dose estradiol animals than in low-dose (p<0.05) or placebo groups (p<0.05). These results indicate that estradiol dose-dependently increases the levels of EPCs in peripheral blood in male animals, improves the recovery of blood flow, and decreases limb necrosis after hind-limb ischemia, and that this enhancement occurs, in part, through augmentation of EPC mobilization and greater incorporation of bone marrow-derived EPCs into foci of neovascularization.

Tracking adult neovascularization during ischemia and inflammation using Vegfr2-LacZ reporter mice.

The vascular endothelial growth factor/vascular endothelial growth factor receptor 2 (VEGF/VEGFR-2) signal transduction system plays a key role during embryonic vascular development and adult neovascularization. In contrast to many endothelial genes, VEGFR-2 is expressed at low levels in most adult vessels but is strongly upregulated during neovascularization, leading to a pro-angiogenic response. Here, we analyzed the activity of regulatory sequences of the murine Vegfr2 gene during neovessel formation in vivo under ischemic and inflammatory conditions. Hindlimb ischemia was induced in transgenic mice, expressing the LacZ reporter gene under the control of Vegfr2 promoter/enhancer elements. Most vessels in the ischemic muscle tissue showed strong endothelium-specific reporter gene expression, whereas nearly no LacZ-expressing capillaries were observed in untreated control tissue. Cutaneous punch wounds were created to induce angiogenesis under inflammatory conditions, leading to robust LacZ expression in the majority of the blood vessels in the wound tissue. Since the cornea is physiologically avascular, the functionality of these promoter/enhancer elements exclusively in newly formed vessels was confirmed using the cornea micropocket assay. Taken together, our results show that these Vegfr2 regulatory elements are active during adult neovessel formation in general. Therefore, these sequences may prove to be valuable targets for novel endothelium-specific anti-angiogenic as well as pro-angiogenic treatment strategies. They may especially allow directing therapeutic gene expression to sites of adult neovascularization. Moreover, the Vegfr2/LacZ reporter mice represent a powerful model to generally analyze the transcriptional control mechanisms involved in the induction of Vegfr2 expression during adult neovascularization.

Enhanced voluntary alcohol consumption after estrogen supplementation negates estrogen-mediated vascular repair in ovariectomized mice.

Preclinical and observational studies in ovariectomized (OVX) animals and pre- and postmenopausal women, respectively, have suggested the cardioprotective effects of estrogen replacement therapy. However, randomized clinical trials have not confirmed estrogen-mediated cardioprotection. Although uncertainties about the duration and optimal type of estrogen replacement regimen might explain the disparity, other factors that may mask the protective effects of 17beta-estradiol (E2) on cardiovascular outcome need scrutiny. Increased ethanol consumption may be one such factor. We examined the effect of E2 supplementation on ethanol consumption in OVX mice and the effect of ethanol consumption on E2-mediated vascular repair, in vivo. OVX mice implanted with E2 pellets consumed significantly more ethanol, compared with those receiving placebo pellets. E2-induced increase in ethanol consumption was not affected by the absence of either estrogen receptor-alpha or -beta. Reendothelialization after carotid artery denudation was repressed, and neovascularization in ischemic hind limbs was blunted in mice consuming ethanol, despite E2 supplementation. In vitro, ethanol dose-dependently attenuated E2-induced endothelial cell (EC) proliferation and tube formation activity and enhanced EC apoptosis, suggesting that ethanol blocks E2-induced EC survival and function. Taken together our data suggest that increased ethanol consumption after E2 supplementation blunts the beneficial effects of E2 on EC function and that novel approaches to estrogen replacement for cardioprotection may benefit from the control of alcohol consumption.

Tumor necrosis factor-alpha receptor p75 is required in ischemia-induced neovascularization.

BACKGROUND: Aging is a risk factor for coronary and peripheral artery disease. Tumor necrosis factor-alpha (TNF-alpha), a proinflammatory cytokine, is expressed in ischemic tissue and is known to modulate angiogenesis. Little is known about the role of TNF-alpha receptors (TNFR1/p55 and TNFR2/p75) in angiogenic signaling. METHODS AND RESULTS: We studied neovascularization in the hindlimb ischemia model in young and old TNFR2/p75 knockout (p75KO) and wild-type age-matched controls. Between days 7 to 10 after hindlimb surgery, 100% of old p75KOs experienced autoamputation of the operated limbs, whereas none of the age-matched wild-type mice exhibited hindlimb necrosis. Poor blood flow recovery in p75KO mice was associated with increased endothelial cell apoptosis, decreased capillary density, and significant reductions in the expression of vascular endothelial growth factor and basic fibroblast growth factor-2 mRNA transcripts in ischemic tissue and in circulating endothelial progenitor cells. The number of circulating bone marrow-derived endothelial progenitor cells was significantly reduced in p75KO mice. Transplantation of wild-type bone marrow mononuclear cells into irradiated old p75KO mice 1 month before hindlimb surgery prevented limb loss. CONCLUSIONS: Our present study suggests that ischemia-induced endothelial progenitor cell-mediated neovascularization is dependent, at least in part, on p75 TNF receptor expressed in bone marrow-derived cells. Specifically, endothelial cell/endothelial progenitor cell survival, vascular endothelial growth factor expression, endothelial progenitor cell mobilization from bone marrow, endothelial progenitor cell differentiation, and ultimately ischemia-induced collateral vessel development are dependent on signaling through TNFR2/p75. Furthermore, because TNFR2/p75 becomes an age-related limiting factor in postischemic recovery, it may be a potential gene target for therapeutic interventions in adult vascular diseases.

Therapeutic angiogenesis inhibits or rescues chemotherapy-induced peripheral neuropathy: taxol- and thalidomide-induced injury of vasa nervorum is ameliorated by VEGF.

Toxic neuropathy represents an important clinical problem in the use of the chemotherapeutic substances Taxol and thalidomide. Sensory neuropathy has a high incidence, lacks an effective treatment and is the dose-limiting factor for these drugs. The pathogenic basis of these neuropathies is unknown. We investigated the hypothesis that the experimental toxic neuropathies from Taxol and thalidomide results from destruction of vasa nervorum and can be reversed by the administration of an angiogenic cytokine. In animal models of Taxol- and thalidomide-induced neuropathy, nerve blood flow has been attenuated and the number of vasa nervorum has been reduced. Intramuscular gene transfer of naked plasmid DNA encoding VEGF-1 administered in parallel with Taxol injections completely inhibited deterioration of nerve function and diminution of the peripheral nerve vasculature. Gene therapy in animals with established Taxol- or thalidomide-induced neuropathies resulted in recovery of vascularity and improved nerve electrophysiology. These findings implicate microvascular damage as the basis for toxic neuropathy and suggest that angiogenic growth factors may constitute a novel treatment for this disorder.

Critical role of endothelial Notch1 signaling in postnatal angiogenesis.

Notch receptors are important mediators of cell fate during embryogenesis, but their role in adult physiology, particularly in postnatal angiogenesis, remains unknown. Of the Notch receptors, only Notch1 and Notch4 are expressed in vascular endothelial cells. Here we show that blood flow recovery and postnatal neovascularization in response to hindlimb ischemia in haploinsufficient global or endothelial-specific Notch1(+/-) mice, but not Notch4(-/-) mice, were impaired compared with wild-type mice. The expression of vascular endothelial growth factor (VEGF) in response to ischemia was comparable between wild-type and Notch mutant mice, suggesting that Notch1 is downstream of VEGF signaling. Treatment of endothelial cells with VEGF increases presenilin proteolytic processing, gamma-secretase activity, Notch1 cleavage, and Hes-1 (hairy enhancer of split homolog-1) expression, all of which were blocked by treating endothelial cells with inhibitors of phosphatidylinositol 3-kinase/protein kinase Akt or infecting endothelial cells with a dominant-negative Akt mutant. Indeed, inhibition of gamma-secretase activity leads to decreased angiogenesis and inhibits VEGF-induced endothelial cell proliferation, migration, and survival. Overexpression of the active Notch1 intercellular domain rescued the inhibitory effects of gamma-secretase inhibitors on VEGF-induced angiogenesis. These findings indicate that the phosphatidylinositol 3-kinase/Akt pathway mediates gamma-secretase and Notch1 activation by VEGF and that Notch1 is critical for VEGF-induced postnatal angiogenesis. These results suggest that Notch1 may be a novel therapeutic target for improving angiogenic response and blood flow recovery in ischemic limbs.

Long-term stable expression of human growth hormone by rAAV promotes myocardial protection post-myocardial infarction.

Recombinant adeno-associated virus (rAAV)-based gene therapy represents a promising approach for the treatment of heart diseases. It has been shown that growth hormone (GH) exerts a favorable effect on cardiovascular function in clinical and animal studies. This study explores a chronic stage after myocardial infarction and the potential therapeutic effects of delivering a human GH gene by rAAV following coronary artery ligation in Sprague-Dawley rats. rAAV vectors stably transduced heart muscle for up to 22 weeks after myocardial infarction (MI). Overexpression of GH via rAAV vectors significantly improved not only cardiac function but also LV pathologic remodeling was attenuated post-MI compared to the control rAAV-lacZ injected group. rAAV-mediated expression of GH also resulted in a significant induction of several angiogenic genes such as eNOS, VEGF and bFGF in rat hearts. Immunohistochemistry revealed an increase in capillary density and proliferation of cells and a decrease in the number of TUNEL-positive cardiomyocytes in the rAAV-GH group. Based on these data, we conclude that rAAV-mediated GH delivery can render a long-term transduction in the infarcted heart and improve cardiac function through promoting angiogenesis and proliferation of cells and protecting cardiomyocytes from ischemia-induced apoptosis.

CD34-positive cells exhibit increased potency and safety for therapeutic neovascularization after myocardial infarction compared with total mononuclear cells.

BACKGROUND: We compared the therapeutic potential of purified mobilized human CD34+ cells with that of mobilized total mononuclear cells (tMNCs) for the preservation/recovery of myocardial tissue integrity and function after myocardial infarction (MI). METHODS AND RESULTS: CD34+ cells were purified from peripheral blood tMNCs of healthy volunteers by magnetic cell sorting after a 5-day administration of granulocyte colony-stimulating factor. Phosphate-buffered saline (PBS), 5x10(5) CD34+ cells/kg, 5x10(5) tMNCs/kg (low-dose MNCs [loMNCs]), or a higher dose of tMNCs (hiMNCs) containing 5x10(5) CD34+ cells/kg was transplanted intramyocardially 10 minutes after the induction of MI in athymic nude rats. Hematoxylin and eosin staining revealed that moderate to severe hemorrhagic MI on day 3 was more frequent in the hiMNC group than in the PBS and CD34+ cell groups. Immunostaining for human-specific CD45 revealed abundant distribution of hematopoietic/inflammatory cells derived from transplanted cells in the ischemic myocardium of the hiMNC group. Capillary density on day 28 was significantly greater in the CD34+ cell group (721.1+/-19.9 per 1 mm2) than in the PBS, loMNC, and hiMNC groups (384.7+/-11.0, 372.5+/-14.1, and 497.5+/-24.0 per 1 mm2) (P<0.01). Percent fibrosis area on day 28 was less in the CD34(+) cell group (15.6+/-0.9%) than in the PBS, loMNC, and hiMNC groups (26.3+/-1.2%, 27.5+/-1.8%, and 22.2+/-1.8%) (P<0.05). Echocardiographic fractional shortening on day 28 was significantly higher in the CD34+ cell group (30.3+/-0.9%) than in the PBS, loMNC, and hiMNC groups (22.7+/-1.5%, 23.4+/-1.1%, and 24.9+/-1.7%; P<0.05). Echocardiographic regional wall motion score was better preserved in the CD34+ cell group (21.8+/-0.5) than in the PBS, loMNC, and hiMNC groups (25.4+/-0.4, 24.9+/-0.4, and 24.1+/-0.6; P<0.05). CONCLUSIONS: CD34+ cells exhibit superior efficacy for preserving myocardial integrity and function after MI than unselected circulating MNCs.