No abstract

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 x 10(6) 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.

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. Support 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 paracrine mechanisms of myocardial protection and functional improvement.

Skeletal and cardiac muscle depend on high turnover of ATP made by mitochondria in order to contract efficiently. The transcriptional coactivator PGC-1alpha has been shown to function as a major regulator of mitochondrial biogenesis and respiration in both skeletal and cardiac muscle, but this has been based only on gain-of-function studies. Using genetic knockout mice, we show here that, while PGC-1alpha KO mice appear to retain normal mitochondrial volume in both muscle beds, expression of genes of oxidative phosphorylation is markedly blunted. Hearts from these mice have reduced mitochondrial enzymatic activities and decreased levels of ATP. Importantly, isolated hearts lacking PGC-1alpha have a diminished ability to increase work output in response to chemical or electrical stimulation. As mice lacking PGC-1alpha age, cardiac dysfunction becomes evident in vivo. These data indicate that PGC-1alpha is vital for the heart to meet increased demands for ATP and work in response to physiological stimuli.

The myocardial phosphocreatine-to-ATP ratio, measured noninvasively with 31P-MR spectroscopy, is a predictor of both total and cardiovascular mortality in patients with dilated cardiomyopathy.

A mouse model of familial hypertrophic cardiomyopathy (FHC) was generated by the introduction of an Arg 403 --> Gln mutation into the alpha cardiac myosin heavy chain (MHC) gene. Homozygous alpha MHC 403/403 mice died 7 days after birth, and sedentary heterozygous alpha MHC 403/+ mice survived for 1 year. Cardiac histopathology and dysfunction in the alpha MHC 403/+ mice resembled human FHC. Cardiac dysfunction preceded histopathologic changes, and myocyte disarray, hypertrophy, and fibrosis increased with age. Young male alpha MHC 403/+ mice showed more evidence of disease than did their female counterparts. Preliminary results suggested that exercise capacity may have been compromised in the alpha MHC 403/+ mice. This mouse model may help to define the natural history of FHC.

Myocytes of the failing heart undergo impressive metabolic remodelling. The time line for changes in the pathways for ATP synthesis in compensated hypertrophy is: flux through the creatine kinase (CK) reaction falls as both creatine concentration ([Cr]) and CK activity fall; increases in [ADP] and [AMP] lead to increases in glucose uptake and utilization; fatty acid oxidation either remains the same or decreases. In uncompensated hypertrophy and in other forms of heart failure, CK flux and fatty acid oxidation are both lower; any increases in glucose uptake and utilization are not sufficient to compensate for overall decreases in the capacity for ATP supply and [ATP] falls. Metabolic remodelling is under transcriptional and post-transcriptional control. The lower metabolic reserve of the failing heart contributes to impaired contractile reserve.

Abstract-Heme oxygenase (HO)-1 degrades the pro-oxidant heme and generates carbon monoxide and antioxidant bilirubin. We have previously shown that in response to hypoxia, HO-1-null mice develop infarcts in the right ventricle of their hearts and that their cardiomyocytes are damaged by oxidative stress. To test whether HO-1 protects against oxidative injury in the heart, we generated cardiac-specific transgenic mice overexpressing different levels of HO-1. By use of a Langendorff preparation, hearts from transgenic mice showed improved recovery of contractile performance during reperfusion after ischemia in an HO-1 dose-dependent manner. In vivo, myocardial ischemia and reperfusion experiments showed that infarct size was only 14.7% of the area at risk in transgenic mice compared with 56.5% in wild-type mice. Hearts from these transgenic animals had reduced inflammatory cell infiltration and oxidative damage. Our data demonstrate that overexpression of HO-1 in the cardiomyocyte protects against ischemia and reperfusion injury, thus improving the recovery of cardiac function. Key Words: heart Ⅲ infarction Ⅲ Langendorff preparation Ⅲ cytoprotection Ⅲ inflammation O xidative stress in the heart caused by ischemia and reperfusion leads to cardiomyocyte death. 1-3 Several studies have shown that increased expression of myocardial stress proteins and/or antioxidant enzymes protects against postischemic injury. 4 -6 In response to stress, elevated expression of heat shock proteins may protect the myocardium. 7 These heat shock proteins are thought to mediate cardioprotection through their biological functions as molecular chaperones by preventing protein denaturation. 7 Heme oxygenase (HO)-1, a stress response and cytoprotective protein, also known as hsp32, protects cells from death due to pathophysiological stress. 8 -12 By degrading the pro-oxidant heme and generating the antioxidant bilirubin, 13,14 HO-1 may protect cells against oxidative injury. In addition, carbon monoxide (CO), another HO-1 reaction product, contributes to the regulation of vascular tone and is reported to have antiinflammatory properties, which may contribute to the cytoprotective action of HO-1. 15,16 HO-1 is upregulated in the heart and blood vessels in response to hemodynamic stress in rats 17,18 and ischemia/ reperfusion injury in pigs, 19,20 implicating an important role for HO-1 in cardiovascular homeostasis. We have recently shown that in response to hypoxia, HO-1-null mice develop right ventricular infarcts with organized mural thrombi. Furthermore, increased lipid peroxidation and oxidative damage occur in right ventricular cardiomyocytes from HO-1-null but not wild-type mice. 12 Thus, we hypothesized that HO-1 may play a central role in cardiac homeostasis by protecting cardiomyocytes from ischemia/reperfusioninduced injury and secondary oxidative damage. To gain insight into the cardioprotective role of HO-1 in vivo, we generated transgenic mice overexpressing HO-1 specifically in the heart. We measured cardiac performance during ...