Unfavourable consequences of chronic cardiac HIF-1α stabilization.

AIMS: The hypoxia-inducible factor-1 (HIF-1) is the master modulator of hypoxic gene expression. The effects of chronically stabilized cardiac HIF-1α and its role in the diseased heart are not precisely known. The aims of this study were as follows: (i) to elucidate consequences of HIF-1α stabilization in the heart; (ii) to analyse long-term effects of HIF-1α stabilization with ageing and the ability of the HIF-1α overexpressing hearts to respond to increased mechanical load; and (iii) to analyse HIF-1α protein levels in failing heart samples. METHODS AND RESULTS: In a cardiac-specific HIF-1α transgenic mouse model, constitutive expression of HIF-1α leads to changes in capillary area and shifts the cardiac metabolism towards glycolysis with a net increase in glucose uptake. Furthermore, Ca(2+) handling is altered, with increased Ca(2)(+) transients and faster intracellular [Ca(2+)] decline. These changes are associated with decreased expression of sarcoplasmic/endoplasmic reticulum calcium ATPase 2a but elevated phosphorylation of phospholamban. HIF-1α transgenic mice subjected to transverse aortic constriction exhibited profound cardiac decompensation. Moreover, cardiomyopathy was also seen in ageing transgenic mice. In parallel, we found an increased stabilization of HIF-1α in heart samples of patients with end-stage heart failure. CONCLUSION: Changes induced with transgenic cardiac HIF-1α possibly mediate beneficial effects in the short term; however, with increased mechanical load and ageing they become detrimental for cardiac function. Together with the finding of increased HIF-1α protein levels in samples from human patients with cardiomyopathy, these data indicate that chronic HIF-1α stabilization drives autonomous pathways that add to disease progression.

Cardiomyocyte-specific prolyl-4-hydroxylase domain 2 knock out protects from acute myocardial ischemic injury.

Prolylhydroxylase domain proteins (PHD) are cellular oxygen-sensing molecules that regulate the stability of the α-subunit of the transcription factor hypoxia inducible factor (HIF)-1. HIF-1 affects cardiac development as well as adaptation of the heart toward increased pressure overload or myocardial infarction. We have disrupted PHD2 in cardiomyocytes (cPhd (-/-)) using Phd2(flox/flox) mice in combination with MLCvCre mice, which resulted in HIF-1α stabilization and activation of HIF target genes in the heart. Although cPhd2(-/-) mice showed no gross abnormalities in cardiac filament structure or function, we observed a significant increased cardiac capillary area in those mice. cPhd2 (-/-) mice did not respond differently to increased mechanical load by transverse aortic constriction compared with their wild-type (wt) littermates. After ligation of the left anterior descending artery, however, the area at risk and area of necrosis were significantly smaller in the cPhd2(-/-) mice compared with Phd2 wt mice in line with the described pivotal role of HIF-1α for tissue protection in case of myocardial infarction. This correlated with a decreased number of apoptotic cells in the infarcted myocardium in the cPhd2(-/-) mice and significantly improved cardiac function 3 weeks after myocardial infarction.

Impaired Ca(2+)-handling in HIF-1alpha(+/-) mice as a consequence of pressure overload.

The hypoxia-inducible factor (HIF)-1 is critically involved in the cellular adaptation to a decrease in oxygen availability. The influence of HIF-1alpha for the development of cardiac hypertrophy and cardiac function that occurs in response to sustained pressure overload has been mainly attributed to a challenged cardiac angiogenesis and cardiac hypertrophy up to now. Hif-1alpha (+/+) and Hif-1alpha (+/-) mice were studied regarding left ventricular hypertrophy and cardiac function after being subjected to transverse aortic constriction (TAC). After TAC, both Hif-1alpha (+/+) and Hif-1alpha (+/-) mice developed left ventricular hypertrophy with increased posterior wall thickness, septum thickness and increased left ventricular weight to a similar extent. No significant difference in cardiac vessel density was observed between Hif-1alpha (+/+) and Hif-1alpha (+/-) mice. However, only the Hif-1alpha (+/-) mice developed severe heart failure as revealed by a significantly reduced fractional shortening mostly due to increased end-systolic left ventricular diameter. On the single cell level this correlated with reduced myocyte shortenings, decreased intracellular Ca(2+)-transients and SR-Ca(2+) content in myocytes of Hif-1a (+/-) mice. Thus, HIF-1alpha can be critically involved in the preservation of cardiac function after chronic pressure overload without affecting cardiac hypertrophy. This effect is mediated via HIF-dependent modulation of cardiac calcium handling and contractility.