Blood vessel growth is mediated by angiogenesis, which is defined as the formation of new blood vessel out of existing vessels, as well as vasculogenesis, a process that circulating progenitor cells contributes to adult neovascularization. Cilostazol, a commercially available drug holding antiplatelet and vasodilating effects, increases intracellular cyclic adenosine monophosphate (cAMP) levels through inhibiting the activity of phosphodiesterase 3. Interestingly, this chemical compound has a lot of cellular effects. In current work, we demonstrated that cilostazol promoted proliferation and migration of human umbilical cord vein endothelial cells (HUVECs), enhanced in-vitro vascular tube formation, and increased releasing of cAMP and NO from them. Furthermore, cilostazol activated eNOS and PI3-K/Akt signaling pathways. We also examined the angiogenic and vasculogenic effects of cilostazol in a murine hindlimb ischemia model. Our data showed that cilostazol enhanced angiogenesis and vasculogenesis with resultant flow recovery after murine hindlimb ischemia partly mediated by promoting mobilization of bone marrow-derived stem cells into circulation and increasing in situ expression of some proteins involved in angiogenesis. In addition, cilostazol significant increased colony forming unit of human endothelial progenitor cells. These results are unique and clinically significant with potential in translational therapy. According to our report, further preclinical and clinical studies of cilostazol on the other ischemic situations such as myocardial infarction will be justified.

Reduction of cardiac myocyte loss and repair of the vasculature post myocardial infarction are important therapeutic goals because the potential for intrinsic repair is limited. Preclinical and limited clinical data support the possibility that bone marrow-derived mesenchymal stem cells may be a suitable cell type for cellular therapy. The goal of this research was to determine the effectiveness of using MSCs from aged mice in cellular therapy for the treatment of AMI. The central hypothesis for this research was that therapeutic potential of mesenchymal stem cells decreases with age. This research utilized global gene expression analysis to investigate molecular differences in MSCs harvested from three different age groups of mice. Microarray analysis was performed to investigate changes in gene expression with respect to aging. Furthermore, both in vitro and in vivo experiments were completed to analyze the functional and molecular characteristics of the MSCs. The data identified age-related defects in mouse MSCs as well as determined the molecular basis for these deficiencies. This study indicates that MSCs from 26m mice are severely deficient in the induction of angiogenesis and cardiac repair due to defective paracrine factor secretion caused by decreased expression of growth factor/cytokine genes. Hypoxia attenuates the deficiency in the aged mice, whereas in young mice low oxygen promotes secretion of paracrine growth factors. It was determined a dysfunction in HIF-1 alpha signaling was present in MSCs from 26m mice and is regulated by the PI3K/Akt signaling in MSCs. Furthermore, two novel and important and novel aspects of this study were the discovery that cell cycle regulation gene expression decreases with age and MSCs have increased insulin resistance with age. Increased insulin resistance in this cell type with aging is likely to have profound effects on the clinical outcomes of using these cells therapeutically. Likewise, loss of cell cycle regulation during proliferation could also lead to undesirable clinical effects. Gaining insight to the repair potential of these cells with respect to age will help to better define future trials of autologous stem cells not only for heart disease but for all of the many applications proposed for these cells.

No description available.

No description available.

Neovascularization, or the formation of blood vessels, is important in both normal physiological processes as well as pathophysiological processes. The main players in neovascularization, endothelial cells (EC), are highly influenced by hemodynamic shear stress and this may play an important role in neovascularization. Two typical types of shear stress found in the vascular system are a unidirectional laminar shear stress (LS) found in straight regions and a disturbed, oscillatory shear stress (OS) found at branches or curves. At the cellular level, LS is thought to promote EC quiescence whereas OS is thought to promote EC dysfunction. Oscillatory sheared EC are pro-proliferative, pro-migratory, and secrete growth factors, all functions important in neovascularization. There are several diseases that involve both disturbed shear stress and neovascularization, such as atherosclerosis, aortic valve disease, and occlusive vascular disease. In these pathophysiological scenarios fluid shear stress may provide a driving force for neovascularization. Therefore, we hypothesized that oscillatory shear stress promotes greater neovascularization compared to unidirectional laminar shear stress through the secretion of angiogenic factors, which play a physiological role in neovascularization in vivo. To test this hypothesis, we first performed tubule formation and migration assays, two important functions in neovessel formation. We found that OS promotes greater tubule formation and migration of EC as compared to LS and this was mediated through secreted factors. Using gene and protein array analysis, we identified Angiopoietin-2 (Ang2) as being upregulated by OS compared to LS in EC. We found that inhibiting Ang2 blocked OS-mediated tubule formation and migration and that LS-inhibited tubule formation could be rescued by addition of Ang2. In addition, Ang2 was found to be upregulated at sites of disturbed flow in vivo, implicating a physiological role for Ang2. To further investigate the physiological role of Ang2 in neovascularization, we examined the effects of inhibiting Ang2 in a mouse model of hindlimb ischemia, which involves both disturbed flow and neovascularization. We found that Ang2 was upregulated in the ischemic adductor muscle suggesting that it plays a role in recovery during hindlimb ischemia. In addition, we found that inhibiting Ang2 decreased blood flow recovery. Ang2 inhibition resulted in decreased smooth muscle cell coverage of vessels as well as decreased macrophage infiltration. These findings suggest that Ang2 promotes blood flow recovery through the recruitment of smooth muscle cells and formation of collaterals, as well as the recruitment of macrophages that secrete important growth factors and help degrade the extracellular matrix in order for neovascularization to occur. In conclusion, this work illustrates the shear stress regulation of neovessel formation through the expression of Ang2, and the role of Ang2 in neovascularization in vivo. By understanding how angiogenic factors are regulated and what role they play in vivo, we can better understand human disease and develop important therapeutic targets.

Diss. (sammanfattning) Stockholm : Karol. inst., 2005. / Härtill 5 uppsatser.

Indiana University-Purdue University Indianapolis (IUPUI) / There is no consensus on which vascular segment or what size of vessels is most important in the process of collateral growth, the degree to which these vessels can enlarge, or the mechanisms that mediate collateral vessel expansion and its impairment. Chapter I identifies the major collateral vessels that develop in response to femoral arterial occlusion in the pig, rat, and mouse hindlimbs for comparison to humans. Pre-existent small named arteries enlarged ~2-3-fold to become the major collateral vessels in each species, these major collaterals displayed characteristics similar to large arteries experiencing flow-mediated outward remodeling, and important differences in vascular wall thickness were observed between rodents and pigs. Chapter II utilized Rac2-/- and Nox2-/- mice to investigate the hypothesis that Nox2-NAD(P)H oxidase is required for major collateral growth subsequent to femoral arterial occlusion. Previous studies suggest bone marrow cell (BMC)-derived reactive oxygen species (ROS) produced by the Nox2 subunit of NAD(P)H oxidase plays an important role in neovascularization and recovery of hindlimb perfusion subsequent to femoral arterial occlusion; but did not investigate collateral growth. The hematopoietic cell restricted protein Rac2 has been shown to bind to and activate Nox2-NAD(P)H oxidase and Rac2-/- and Nox2-/- leukocytes display impaired ROS related functions. The data demonstrated that Rac2 and Nox2 are not essential for major collateral growth, but both are important for the recovery of hindlimb perfusion and preservation of distal tissue morphology. Chapter III investigated BMC and antioxidant therapy in the age-related impairment of collateral growth. Aging, like all cardiovascular disease risk factors is associated with elevated ROS and impaired collateral growth. Studies also suggest BMCs promote collateral growth by secreting paracrine factors but elevated ROS may affect the efficacy of BMCs. The data revealed that neither BMC injection nor antioxidant therapy via apocynin enhanced the process of major collateral artery growth in aged mice.

Peripheral artery disease (PAD) affects more than 200 million people worldwide. PAD refers to illness due to a reduction or complete occlusion of blood flow in the artery, especially to the extremities in disease conditions, such as atherosclerosis or diabetes. Critical limb ischemia (CLI) is a severe form of PAD associated with high morbidity and mortality. Currently, no effective and permanent treatments are available for this disease. The current endovascular medications (e.g., angioplasty or stents) only relieve the clinical symptoms while the surgical therapies (e.g., bypass or endarterectomy) require grafting vessels from a healthy organ to the diseased limb of the patient. However, even with these therapeutic techniques, 30% of patients still undergo limb amputation within a year. Thus, understanding of disease mechanism and development of new therapeutic approaches are in urgent needs. Meis1 (myeloid ecotropic viral integration site 1) gene belongs to the three-amino-acid loop extension subclass of homeobox gene families, and it is a highly conserved transcription factor in all eukaryotes. Up to date, little is known about the role of Meis1 in regulating vascular remodeling under ischemic condition. In this study, we aim to investigate the role and underlying mechanism of Meis1 in the regulation of arteriogenesis and angiogenesis using hindlimb ischemia model of transgenic neonatal mice. The long-term goal is to develop a new treatment for patients with PAD. Three separate but related studies were planned to complete the proposed research aims. To better understand the role of Meis1, we reviewed, in the first chapter, all literature relevant to the recent advances of the Meis1 in normal hematopoiesis, vasculogenesis, and heart developments, which were mostly studied in zebrafish and mouse. Briefly, Meis1 is found to be highly expressed in the brain and retina in zebrafish and additional in the heart, nose, and limb in mouse during the very early developmental stage, and remains at a low level quickly after birth. Meis1 is necessary for both primitive and definitive hematopoiesis and required for posterior erythroid differentiation. The absence of Meis1 results in a severe reduction of the number of mature erythrocytes and weakens the heart beats in zebrafish. Meis1 deficiency mouse is dead as early as E11.5 due to the severe internal hemorrhage. In addition, Meis1 is essential in heart development. Knock-down of Meis1 can promote angiotensin II-induced cardiomyocytes (CMs) hypertrophy or CMs proliferation, which can be repressed by a transcription factor Tbx20. Meis1 appears to play a complicated role in the blood vessels. Although the major blood vessels are still normal when global deletion of Meis1, the intersegmental vessel cannot be formed in Meis1 morphants in the zebrafish, and the small vessels are either too narrow or form larger sinuses in Meis1 deficient mouse. The effects of Meis1 on the vascular network under normal and disease (ischemia) condition remain largely unknown, and the existing data in this field is limited. In the second chapter, we developed a method protocol to identify mice of all ages, especially neonates that we faced methodological difficulties to easily and permanently label prior to our major experiments. In this study, single- or 2-color tattooing (ear, tail, or toe or combinations) was performed to identify a defined or unlimited number of mice, respectively. Tail tattooing using both green and red pastes was suitable for identifying white-haired neonatal mice as early as postnatal day (PND) 1, whereas toe tattooing with green paste was an effective alternative approach for labeling black-haired mouse pups. In comparison, single-color (green) or 2-color (green and red) ear tattooing identified both white and black adult mice older than three weeks. Ear tattooing can be adapted to labeling an unlimited number of adult mice by adding the cage number. Thus, tattooing various combinations of the ears, tail, and toes provides an easy and permanent approach for identifying mice of all ages with minimal disturbance to the animals, which shows a new approach than any existing method to identify mouse at all ages, especially the neonatal pups used in the present study (Chapter 4). Various formation of hindlimb ischemia with ligations of femoral artery or vein or both have been reported in the literature. The ischemic severity varies dependent on mouse strains and ligation methods. Due to the tiny body size of our experimental neonatal mice (PND2), it is technically challenging to separate the femoral artery from femoral vein without potential bleeding. In the third chapter, we aimed to explore a suitable surgical approach that can apply to neonatal mice. To this end, we compared the effects of femoral artery/vein (FAV) excision vs. femoral artery (FA) excision on hindlimb model using adult CD-1 mice. We showed during the 4-week period of blood reperfusion, no statistically significant differences were found between FAV and FA excision-induced ischemia regarding the reduction of limb blood flow, paw size, number of necrotic toes, or skeletal muscle cell size. We conclude that FAV and FA excision in CD-1 mice generate a comparable severity of hindlimb ischemia. In other words, FAV ligation is no more severe than FA ligation. These findings provide valuable information for researchers when selecting ligation methods for their neonate hindlimb models. Based on these findings, we selected FAV ligation of hindlimb ischemia approach to study the function of Meis1 in vascular remodeling of neonatal mice. In the fourth chapter (the main part of my dissertation), we investigated the roles of Meis1 in regulating arteriogenesis and angiogenesis of neonatal mouse under the ischemic condition. To this end, endothelial cell-specific deletion of Meis1 was generated by cross-breeding Meis1flox/flox mice with Tie2-Cre mice. Wild-type (WT, Meis1f/f) and endothelial cell-specific knock-out (KO, Meis1ec-/-Tie2-Cre+) C57BL/6 mice at the age of PND2 were used. Under the anesthesia, the pups were subject to hindlimb ischemia by excising FAV. Laser Doppler Imager was used to measure the blood flow pre- and post-surgery up to 28 days. Toe necrosis, skeletal regeneration, and vascular distributions were examined at the end of experiments (PND28 post-ischemia). Surprisingly, during 4-week periods after ischemia, the blood flow ratios (ischemic vs. control limb) in KO mice significantly increased compared to WT on PND14 and PND28, suggesting the inhibitory effects of Meis1 on blood flow recovery under ischemic condition. Meanwhile, WT mice showed more severe necrotic limb (lower ratio of limb length and area, and higher necrotic scores at PND7) than those in the KO mice. Furthermore, significant increases in diameters of Dil-stained arterioles of the skin vessel and the vessels on the ligation site were observed in KO mice, indicating the enhanced arteriogenesis in KO mice. To investigate the underlying mechanism, RNA from the ischemia and control limb was extracted and q-PCR was used to study the potential genes involved in the mechanism. Casp3 and Casp8 were found downregulated showing less apoptosis in the KO mice. On the other hand, endothelial cells (ECs) were isolated from the lungs of 3-5 WT and KO neonates using CD31 Microbeads. CD31+ cells were plated and treated with 0, 0.5, and 1μM doxorubicin for 24 hours and analyzed with various assays. Meis1-KO ECs demonstrated higher cell viability and formed a higher number of vascular tubes than those in WT ECs following 0.5μM Dox treatment, presenting the potential ability of angiogenesis in KO-ECs. Furthermore, the increased viability in KO ECs may be due to the decreased expression or activities of Casp8 and Casp3. In conclusion, my present studies have developed a new methodology to easily and permanently identify all mice at any ages. The insignificant differences between FAV and FA ligations suggest that a relative-easy surgical approach could be used to generate hindlimb ischemic model, which potentially reduces the cost, decreases the surgical time and prevents damage of femoral nerve from surgical tools. More importantly, by using transgenic mice, we found that Meis1-KO dramatically increased blood flow and protected the ischemic hindlimb through vascular remodeling. Obviously, the molecular and cellular mechanisms underlying the above beneficial effects appear complicated and likely to involve multiple cellular remodeling processes and molecular signaling pathways to enhance arteriogenesis and angiogenesis and/or reduce cellular apoptosis through Meis1-mediated pathways. Our study demonstrated that under ischemic condition, knockout of Meis1 increases expression of Hif1a, which then activates Agt or VEGF, thus enhances arteriogenesis or angiogenesis; In addition, knockout of Meis1 activates Ccnd1, which subsequently promotes regeneration of skeletal muscle, and reduces expression of Casp8 and Casp3, thus preventing limb tissue from ischemia-induced apoptosis. Our innovative findings offer great potential to ultimately lead to new drug discovery or therapeutic approaches for prevention or treatment of PAD. / PHD

La thérapie cellulaire suscite de grands espoirs dans le domaine cardiovasculaire. Cependant les premières études humaines sont décevantes. Parmi les explications avancées, citons un mauvais choix de cellules, une méthode de délivrance inadéquate, une préparation des cellules et des tissus hôtes insuffisante ou une trop grande mortalité cellulaire après injection.Durant ce travail nous avons voulu explorer 3 pistes d’optimisation de la thérapie cellulaire à visée pro-angiogénique utilisant les cellules souches mésenchymateuses (MSC) et contribué à l’exploration des mécanismes mis en jeu, en particulier en explorant le rôle du système Wnt/Frizzled.Nous avons tout d’abord étudié un système original de délivrance de cellules utilisant un « patch » musculaire cousu en regard d’un myocarde infarci de souris. Puis nous avons étudié l’effet d’une surexpression de sFRP1, inhibiteur de la voie Wnt, sur un modèle de matrice sous cutanée. Enfin, nous avons testé l’hypothèse qu’un préconditionnement hypoxique des cellules permettrait une meilleure survie cellulaire et améliorerait la réparation vasculaire et tissulaire après ischémie de patte chez la souris.Nos résultats permettent notamment de montrer que les MSC ont des capacités d’invasion des tissus ischémiques et qu’elles se différencient en péricytes en formant un réseau tridimensionnel de soutien aux cellules endothéliales. Par ailleurs, via sFRP1, nous mettons en évidence un rôle du système Wnt/Fzd dans l’effet pro-angiogénique. Enfin, nous montrons l’intérêt du préconditionnement hypoxique dont les effets sont médiés par Wnt4.L’ensemble de ces données permet d’envisager des voies d’optimisation de la thérapie cellulaire. / Some of the challenges facing stem-cell therapy for cardiac disease are which type of stem cell or progenitor cell is the best candidate for therapy, how to survive in the low oxygen environment of ischemic myocardium. Here we studied the potential of mesenchymal stem cells (MSCs) as vascular progenitor cells in vitro and in vivo, and we studied the effects of sFRP-1/Wnt signaling modulation or hypoxia on MSC properties. First, we demonstrated the beneficial effect of MSC application on ischemic heart repair using an original surgical model (patch) to deliver stem cells. This study showed that the contribution of the MSCs in the mouse infarcted myocardium was beneficial either on the scar (increase in angiogenesis, in cell proliferation, reduction in ventricular remodeling) or on the trophicity of the patch.Then we characterized the angiogenic properties of MSC in vitro and in vivo. Our data demonstrate that MSCs could be recruited and formed vascular structures around endothelial tubes. We showed in vivo that the surexpression of sFRP-1 (regulating factor of the Wnt system) in MSCs increased their potential of pericyte-like cells correlated with an increased maturation of the vessels via an intracellular GSK-3 dependent pathway in MSCs. Our next objective was to investigate the effects of hypoxia exposure on MSC before implantation for vascular and tissue regeneration in mice with hind limb ischemia. Our data suggest that hypoxic preconditioning has a critical role on MSC dynamic functions, shifting MSC location in situ to enhance ischemic tissue recovery, facilitating vascular cell mobilization and skeletal myoblast regeneration via a paracrine Wnt dependent mechanism.