Victor J. Dzau

Mesenchymal stem cells modified with Akt prevent remodeling and restore performance of infarcted hearts

Transplantation of adult bone marrow–derived mesenchymal stem cells has been proposed as a strategy for cardiac repair following myocardial damage. However, poor cell viability associated with transplantation has limited the reparative capacity of these cells in vivo. In this study, we genetically engineered rat mesenchymal stem cells using ex vivo retroviral transduction to overexpress the prosurvival gene Akt1 (encoding the Akt protein). Transplantation of 5 × 106 cells overexpressing Akt into the ischemic rat myocardium inhibited the process of cardiac remodeling by reducing intramyocardial inflammation, collagen deposition and cardiac myocyte hypertrophy, regenerated 80–90% of lost myocardial volume, and completely normalized systolic and diastolic cardiac function. These observed effects were dose (cell number) dependent. Mesenchymal stem cells transduced with Akt1 restored fourfold greater myocardial volume than equal numbers of cells transduced with the reporter gene lacZ. Thus, mesenchymal stem cells genetically enhanced with Akt1 can repair infarcted myocardium, prevent remodeling and nearly normalize cardiac performance.

Paracrine Mechanisms in Adult Stem Cell Signaling and Therapy

Animal and preliminary human studies of adult cell therapy following acute myocardial infarction have shown an overall improvement of cardiac function. Myocardial and vascular regeneration have been initially proposed as mechanisms of stem cell action. However, in many cases, the frequency of stem cell engraftment and the number of newly generated cardiomyocytes and vascular cells, either by transdifferentiation or cell fusion, appear too low to explain the significant cardiac improvement described. Accordingly, we and others have advanced an alternative hypothesis: the transplanted stem cells release soluble factors that, acting in a paracrine fashion, contribute to cardiac repair and regeneration. Indeed, cytokines and growth factors can induce cytoprotection and neovascularization. It has also been postulated that paracrine factors may mediate endogenous regeneration via activation of resident cardiac stem cells. Furthermore, cardiac remodeling, contractility, and metabolism may also be influenced in a paracrine fashion. This article reviews the potential paracrine mechanisms involved in adult stem cell signaling and therapy.

Paracrine action accounts for marked protection of ischemic heart by Akt-modified mesenchymal stem cells

Paracrine action accounts for marked protection of ischemic heart by Akt-modified mesenchymal stem cells

Impaired vasodilation of forearm resistance vessels in hypercholesterolemic humans.

The effect of hypercholesterolemia on vascular function was studied in humans. To eliminate the potential confounding effects of atherosclerosis, vascular reactivity was measured in the forearm resistance vessels of 11 normal subjects (serum LDL cholesterol = 111 +/- 7 mg/dl) and 13 patients with hypercholesterolemia (serum LDL cholesterol = 211 +/- 19 mg/dl, P less than 0.05). Each subject received intrabrachial artery infusions of methacholine, which releases endothelium-derived relaxant factor, and nitroprusside which directly stimulates guanylate cyclase in vascular smooth muscle. Maximal vasodilatory potential was determined during reactive hyperemia. Vasoconstrictive responsiveness was examined during intra-arterial phenylephrine infusion. Forearm blood flow was determined by venous occlusion plethysmography. Basal forearm blood flow in normal and hypercholesterolemic subjects was comparable. Similarly, reactive hyperemic blood flow did not differ between the two groups. In contrast, the maximal forearm blood flow response to methacholine in hypercholesterolemic subjects was less than that observed in normal subjects. In addition, the forearm blood flow response to nitroprusside was less in hypercholesterolemic subjects. There was no difference in the forearm vasoconstrictive response to phenylephrine in the two groups. Thus, the vasodilator responses to methacholine and nitroprusside were blunted in patients with hypercholesterolemia. We conclude that in humans with hypercholesterolemia, there is a decreased effect of nitrovasodilators, including endothelium-derived relaxing factor, on the vascular smooth muscle of resistance vessels.

Evidence supporting paracrine hypothesis for Akt-modified mesenchymal stem cell-mediated cardiac protection and functional improvement

We previously reported that intramyocardial injection of bone marrow‐derived mesenchymal stem cells overexpressing Akt (Akt‐MSCs) inhibits ventricular remodeling and restores cardiac function measured 2 wk after myocardial infarction. Here, we report that the functional improvement occurs in < 72 h. This early remarkable effect cannot be readily attributed to myocardial regeneration from the donor cells. Thus, we hypothesized that paracrine actions exerted by the cells through the release of soluble factors might be important mechanisms of tissue repair and functional improvement after injection of the Akt‐MSCs. Indeed, in the current study we demonstrate that conditioned medium from hypoxic Akt‐MSCs markedly inhibits hypoxia‐induced apoptosis and triggers vigorous spontaneous contraction of adult rat cardiomyocytes in vitro. When injected into infarcted hearts, the Akt‐MSC conditioned medium significantly limits infarct size and improves ventricular function relative to controls. Sup‐port to the paracrine hypothesis is provided by data showing that several genes, coding for factors (VEGF, FGF‐2, HGF, IGF‐I, and TB4) that are potential mediators of the effects exerted by the Akt‐MSC conditioned medium, are significantly up‐regulated in the Akt‐MSCs, particularly in response to hypoxia. Taken together, our data support Akt‐MSC‐mediated para‐crine mechanisms of myocardial protection and functional improvement.‐Gnecchi, M., He, H., Noiseux, N., Liang, O. D., Zhang, L., Morello, F., Mu, H., Melo, L. G., Pratt, R. E., Ingwall, J. S., Dzau, V. J. Evidence supporting paracrine hypothesis for Akt‐modified mes‐enchymal stem cell‐mediated cardiac protection and functional improvement. FASEB J. 20, 661–669 (2006)

L-arginine improves endothelium-dependent vasodilation in hypercholesterolemic humans.

Endothelium-dependent vasodilation is impaired in hypercholesterolemia, even before the development of atherosclerosis. The purpose of this study was to determine whether infusion of L-arginine, the precursor of the endothelium-derived relaxing factor, nitric oxide, improves endothelium-dependent vasodilation in hypercholesterolemic humans. Vascular reactivity was measured in the forearm resistance vessels of 11 normal subjects (serum LDL cholesterol = 2.76 +/- 0.10 mmol/liter) and 14 age-matched patients with hypercholesterolemia (serum LDL cholesterol = 4.65 +/- 0.36 mmol/liter, P < 0.05). The vasodilative response to the endothelium-dependent vasodilator, methacholine chloride, was depressed in the hypercholesterolemic group, whereas endothelium-independent vasodilation, induced by nitroprusside, was similar in each group. Intravenous administration of L-arginine augmented the forearm blood flow response to methacholine in the hypercholesterolemic individuals, but not in the normal subjects. L-arginine did not alter the effect of nitroprusside in either group. D-arginine had no effect on forearm vascular reactivity in either group. It is concluded that endothelium-dependent vasodilation is impaired in hypercholesterolemic humans. This abnormality can be improved acutely by administration of L-arginine, possibly by increasing the synthesis of endothelium-derived relaxing factor.

Recent Progress in Angiotensin II Type 2 Receptor Research in the Cardiovascular System

Angiotensin II (Ang II) plays an important role in regulating cardiovascular hemodynamics and structure. Multiple lines of evidence have suggested the existence of Ang II receptor subtypes, and at least 2 distinct receptor subtypes have been defined on the basis of their differential pharmacological and biochemical properties and designated as type 1 (AT1) and type 2 (AT2) receptors. To date, most of the known effects of Ang II in adult tissues are attributable to the AT1 receptor. Recent cloning of the AT2 receptor contributes to reveal its physiological functions, but many functions of the AT2 receptor are still an enigma. AT1 and AT2 receptors belong to the 7-transmembrane, G protein-coupled receptor family. However, accumulating evidence demonstrates that the function and signaling mechanisms of these receptor subtypes are quite different, and these receptors may exert opposite effects in terms of cell growth and blood pressure regulation. We will review the role of the AT2 receptor in the cardiovascular system and the molecular and cellular mechanisms of AT2 receptor action.

Tissue Angiotensin and Pathobiology of Vascular Disease: A Unifying Hypothesis

There is increasing evidence that direct pathobiological events in the vessel wall play an important role in vascular disease. An important mechanism involves the perturbation of the homeostatic balance between NO and reactive oxygen species. Increased reactive oxygen species can inactivate NO and produce peroxynitrite. Angiotensin II is a potent mediator of oxidative stress and stimulates the release of cytokines and the expression of leukocyte adhesion molecules that mediate vessel wall inflammation. Inflammatory cells release enzymes (including ACE) that generate angiotensin II. Thus, a local positive-feedback mechanism could be established in the vessel wall for oxidative stress, inflammation, and endothelial dysfunction. Angiotensin II also acts as a direct growth factor for vascular smooth muscle cells and can stimulate the local production of metalloproteinases and plasminogen activator inhibitor. Taken together, angiotensin II can promote vasoconstriction, inflammation, thrombosis, and vascular remodeling. In this article, we propose a model that unifies the interrelationship among cardiovascular risk factors, angiotensin II, and the pathobiological mechanisms contributing to cardiovascular disease. This model may also explain the beneficial effects of ACE inhibitors on cardiovascular events beyond blood pressure reduction.Abstract —There is increasing evidence that direct pathobiological events in the vessel wall play an important role in vascular disease. An important mechanism involves the perturbation of the homeostatic balance between NO and reactive oxygen species. Increased reactive oxygen species can inactivate NO and produce peroxynitrite. Angiotensin II is a potent mediator of oxidative stress and stimulates the release of cytokines and the expression of leukocyte adhesion molecules that mediate vessel wall inflammation. Inflammatory cells release enzymes (including ACE) that generate angiotensin II. Thus, a local positive-feedback mechanism could be established in the vessel wall for oxidative stress, inflammation, and endothelial dysfunction. Angiotensin II also acts as a direct growth factor for vascular smooth muscle cells and can stimulate the local production of metalloproteinases and plasminogen activator inhibitor. Taken together, angiotensin II can promote vasoconstriction, inflammation, thrombosis, and vascular remodeling. In this article, we propose a model that unifies the interrelationship among cardiovascular risk factors, angiotensin II, and the pathobiological mechanisms contributing to cardiovascular disease. This model may also explain the beneficial effects of ACE inhibitors on cardiovascular events beyond blood pressure reduction.

Vascular proliferation and atherosclerosis: New perspectives and therapeutic strategies

In atherosclerosis, the vascular smooth muscle cell (VSMC) contributes to vessel wall inflammation and lipoprotein retention, as well as to the formation of the fibrous cap that provides stability to the plaque. The VSMC can undergo a proliferative response that underlies the development of in-stent restenosis, bypass graft occlusion and transplant vasculopathy. Although the benefit/risk of therapeutic inhibition of VSMC proliferation in atherosclerosis is unclear, experimental and human evidence strongly suggests the therapeutic potential of antiproliferative therapy for in-stent restenosis, bypass graft failure and other vascular proliferative disorders.

Genetic mapping of a gene causing hypertension in the stroke-prone spontaneously hypertensive rat.

The stroke-prone spontaneously hypertensive rat (SHRSP) is a well-characterized model for primary hypertension in humans. High blood pressure in SHRSP shows polygenic inheritance, but none of the loci responsible have previously been identified. To locate genes controlling this quantitative trait, we mapped a large collection of DNA polymorphisms in a cross between SHRSP and the normotensive WKY strain. Here we report strong genetic evidence that a gene, Bp1, having a major effect on blood pressure maps to rat chromosome 10 with a LOD score of 5.10 and is closely linked to the rat gene encoding angiotensin-converting enzyme (ACE), an enzyme that plays a major role in blood pressure homeostasis and is an important target of anti-hypertensive drugs. We also find significant, albeit weaker, linkage to a locus, Bp2, on chromosome 18. We discuss the implications of genetic dissection of quantitative disease-related phenotypes in mammals.