Contribution of hypoxia to the development of cardiomyopathy in hamsters

Gene network analysis to determine the effect of hypoxia-associated genes on brain damages and tumorigenesis using an avian model

BACKGROUND

Hypoxia refers to the condition of low oxygen pressure in the atmosphere and characterization of response to hypoxia as a biological complex puzzle, is challenging. Previously, we carried out a comparative genomic study by whole genome resequencing of highland and lowland Iranian native chickens to identify genomic variants associated with hypoxia conditions. Based on our previous findings, we used chicken as a model and the identified hypoxia-associated genes were converted to human's orthologs genes to construct the informative gene network. The main goal of this study was to visualize the features of diseases due to hypoxia-associated genes by gene network analysis.

RESULTS

It was found that hypoxia-associated genes contained several gene networks of disorders such as Parkinson, Alzheimer, cardiomyopathy, drug toxicity, and cancers. We found that biological pathways are involved in mitochondrion dysfunctions including peroxynitrous acid production denoted in brain injuries. Lewy body and neuromelanin were reported as key symptoms in Parkinson disease. Furthermore, calmodulin, and amyloid precursor protein were detected as leader proteins in Alzheimer's diseases. Dexamethasone was reported as the candidate toxic drug under the hypoxia condition that implicates diabetes, osteoporosis, and neurotoxicity. Our results suggested DNA damages caused by the high doses of UV radiation in high-altitude conditions, were associated with breast cancer, ovarian cancer, and colorectal cancer.

CONCLUSIONS

Our results showed that hypoxia-associated genes were enriched in several gene networks of disorders including Parkinson, Alzheimer, cardiomyopathy, drug toxicity, and different types of cancers. Furthermore, we suggested, UV radiation and low oxygen conditions in high-altitude regions may be responsible for the variety of human diseases.

Exome array analysis identifies GPR35 as a novel susceptibility gene for anthracycline-induced cardiotoxicity in childhood cancer

OBJECTIVES

Pediatric cancer survivors are a steadily growing population; however, chronic anthracycline-induced cardiotoxicity (AIC) is a serious long-term complication leading to considerable morbidity. We aimed to identify new genes and low-frequency variants influencing the susceptibility to AIC for pediatric cancer patients.

PATIENTS AND METHODS

We studied the association of variants on the Illumina HumanExome BeadChip array in 83 anthracycline-treated pediatric cancer patients. In addition to single-variant association tests, we carried out a gene-based analysis to investigate the combined effects of common and low-frequency variants to chronic AIC.

RESULTS

Although no single-variant showed an association with chronic AIC that was statistically significant after correction for multiple testing, we identified a novel significant association for G protein-coupled receptor 35 (GPR35) by gene-based testing, a gene with potential roles in cardiac physiology and pathology (P=7.0×10), which remained statistically significant after correction for multiple testing (PFDR=0.03). The greatest contribution to this observed association was made by rs12468485, a missense variant (p.Thr253Met, c.758C>T, minor allele frequency=0.04), with the T allele associated with an increased risk of chronic AIC and more severe symptomatic cardiac manifestations at low anthracycline doses.

CONCLUSION

Using exome array data, we identified GPR35 as a novel susceptibility gene associated with chronic AIC in pediatric cancer patients.

Upregulated expression of cardiac ankyrin repeat protein in human failing hearts due to arrhythmogenic right ventricular cardiomyopathy

AIMS

Expression of cardiac ankyrin repeat protein (CARP) is augmented in heart failure due to dilated or ischaemic cardiomyopathy. It is unclear whether CARP is upregulated in heart failure due to arrhythmogenic right ventricular cardiomyopathy (ARVC). In the present study, we investigated the expression pattern of CARP and the correlation between CARP and the well-known heart failure marker pro-atrial natriuretic peptide (proANP) in ARVC failing hearts.

METHODS AND RESULTS

Gene microarray analysis demonstrated increased CARP expression in ARVC failing hearts compared with non-failing control hearts, which was further validated by real-time RT-PCR, western blot, and ELISA at the mRNA and protein levels. Fractionation experiments revealed that the upregulation of CARP expression is restricted to the nuclei of residual cardiac cells in ARVC failing hearts. Regression analysis showed a positive correlation between CARP and proANP in ARVC failing hearts.

CONCLUSION

Augmented CARP expression may be a common molecular event in failing hearts regardless of cardiomyopathic aetiology. The upregulation of nuclear CARP expression and positive correlation between cardiac CARP and proANP suggests that CARP may be used as a genetic marker existing in the nuclei in contrast to proANP existing in the cytosol of cardiac cells in heart failure patients.

Animal models of cardiac disease: potential usefulness for studying health effects of inhaled particles

Cardiac disease is one of the major causes of morbidity and mortality worldwide and is the leading cause of death in the United States. Epidemiologic studies have shown a close association between morbidity and mortality from cardiac disease, primarily in persons already affected, and with modest increases in levels of air pollution. At present, no mechanisms are known by which inhaled air pollutants interact with the heart to cause death. Thus, animal models of cardiac disease are needed to study possible interactions between inhaled pollutants and the heart and the resultant morbidity and mortality. Very little research in animals has been conducted in this area, and appropriate animal models must be carefully selected. The purpose of this review is to examine several potential animal models and to discuss their advantages and disadvantages in the study of cardiac disease and air pollution.

Sp1 increases expression of cyclooxygenase-2 in hypoxic vascular endothelium. Implications for the mechanisms of aortic aneurysm and heart failure

Cyclooxygenase-2 (COX-2) catalyzes prostaglandin synthesis from arachidonic acid and is expressed locally in aortic aneurysm and heart failure. Cellular hypoxia is also found in these conditions. We have previously shown that cox-2 is transcriptionally regulated by hypoxia in human umbilical vein endothelial cells (HUVEC) in culture via the transactivation factor NF-kappaB p65, leading to increased production of prostaglandin E(2), an inhibitor of vascular smooth muscle cell proliferation. Sp1 is a transactivation factor known to be important in the regulation of cytokine expression in association with NF-kappaB. We hypothesized that Sp1 is involved in the induction of cox-2 in hypoxic HUVEC. Electrophoretic mobility shift assays with hypoxic HUVEC nuclear protein showed that both Sp1 and the related protein Sp3 specifically bound to the cox-2 promoter. Immunoblotting demonstrated that hypoxia increased the nuclear localization of Sp1 but did not change the Sp3 content in HUVEC. Overexpression of Sp1 through transfection of HUVEC enhanced cox-2 promoter activity as measured by reporter gene expression and by the production of COX-2. The specificity of the results was confirmed by mutation of the Sp1-binding site in the cox-2 promoter construct and by reproducibility in an Sp-deficient Drosophila SL2 cell line. The regulatory role of Sp1 discovered in this work supports the concept that a mechanistic link exists between vascular cellular hypoxia and mediators of inflammation associated with aortic aneurysm and heart failure.

The potential for myocardial imaging with hypoxia markers

Direct "hot spot" imaging of myocardial tissue hypoxia is potentially of great clinical importance because available noninvasive approaches for the detection of myocardial ischemia have generally been based on the detection of flow heterogeneity or identification of regional alterations of myocardial metabolism. These existing approaches provide only an indirect assessment of regional myocardial ischemia, and may be affected by either sympathetic activation or substrate availability. The assessment of tissue oxygenation with hypoxic compounds may be the best indicator of the balance of flow and oxygen consumption. These compounds may provide a means of identifying dysfunctional chronically ischemic but viable "hibernating" myocardium and find a critical place in the assessment of angiogenesis. Nitroimidazole compounds hold promise for positive imaging of hypoxia in the heart. However, refinement of these compounds is needed to improve target specificity. The potential of technetium-99m (Tc99m) complexes derived from removal of the nitroimidazole moiety from a nitroimidazole-containing ligand is interesting and warrants further investigation. Experimental studies support the possibility of identifying myocardial hypoxia with the positron-emitting compound F18-fluoromisonidazole noninvasively. The potential of a Tc99m labeled nitroimidazole for positive imaging of myocardial ischemia is tremendous because single-photon imaging is more widely available. The true clinical potential of these nitroimidazole compounds can only be defined with future experimental and clinical studies. Ideally, these studies should include comparisons of tracer uptake with independent measures of regional ischemia or measures of oxygen tension, potentially using magnetic resonance imaging.