Cardiac rupture is a fatal complication of acute myocardial infarction lacking treatment. Here, acute myocardial infarction resulted in rupture in wild-type mice and in mice lacking tissue-type plasminogen activator, urokinase receptor, matrix metalloproteinase stromelysin-1 or metalloelastase. Instead, deficiency of urokinase-type plasminogen activator (u-PA-/-) completely protected against rupture, whereas lack of gelatinase-B partially protected against rupture. However, u-PA-/- mice showed impaired scar formation and infarct revascularization, even after treatment with vascular endothelial growth factor, and died of cardiac failure due to depressed contractility, arrhythmias and ischemia. Temporary administration of PA inhibitor-1 or the matrix metalloproteinase-inhibitor TIMP-1 completely protected wild-type mice against rupture but did not abort infarct healing, thus constituting a new approach to prevent cardiac rupture after acute myocardial infarction.

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The molecular mechanisms predisposing to atherosclerotic aneurysm formation remain undefined. Nevertheless, rupture of aortic aneurysms is a major cause of death in Western societies, with few available treatments and poor long-term prognosis. Indirect evidence suggests that matrix metalloproteinases (MMPs) and plasminogen activators (PAs) are involved in its pathogenesis. MMPs are secreted as inactive zymogens (pro-MMPs), requiring activation in the extracellular compartment. Plasmin, generated from the zymogen plasminogen by tissue-type plasminogen activator (t-PA) or urokinase-type plasminogen activator (u-PA; refs 14,15), has been proposed as a possible activator in vitro, but evidence for such a role in vivo is lacking. Analysis of atherosclerotic aorta in mice with a deficiency of apoliprotein E (Apoe-/-; ref. 18), singly or combined with a deficiency of t-PA (Apoe-/-:Plat-/-) or of u-PA (Apoe-/-:Plau-/-; ref. 19), indicated that deficiency of u-PA protected against media destruction and aneurysm formation, probably by means of reduced plasmin-dependent activation of pro-MMPs. This genetic evidence suggests that plasmin is a pathophysiologically significant activator of pro-MMPs in vivo and may have implications for the design of therapeutic strategies to prevent aortic-wall destruction by controlling Plau gene function.

HIF prolyl hydroxylases (PHD1-3) are oxygen sensors that regulate the stability of the hypoxia-inducible factors (HIFs) in an oxygen-dependent manner. Here, we show that loss of Phd1 lowers oxygen consumption in skeletal muscle by reprogramming glucose metabolism from oxidative to more anaerobic ATP production through activation of a Pparalpha pathway. This metabolic adaptation to oxygen conservation impairs oxidative muscle performance in healthy conditions, but it provides acute protection of myofibers against lethal ischemia. Hypoxia tolerance is not due to HIF-dependent angiogenesis, erythropoiesis or vasodilation, but rather to reduced generation of oxidative stress, which allows Phd1-deficient myofibers to preserve mitochondrial respiration. Hypoxia tolerance relies primarily on Hif-2alpha and was not observed in heterozygous Phd2-deficient or homozygous Phd3-deficient mice. Of medical importance, conditional knockdown of Phd1 also rapidly induces hypoxia tolerance. These findings delineate a new role of Phd1 in hypoxia tolerance and offer new treatment perspectives for disorders characterized by oxidative stress.

We have identified and characterized a new orphan member of the nuclear hormone receptor superfamily, called MB67, which is predominantly expressed in liver. MB67 binds and transactivates the retinoic acid response elements that control expression of the retinoic acid receptor P2 and alcohol dehydrogenase 3 genes, both of which consist of a direct repeat hexamers related to the consensus AGGTCA, separated by 5 bp. MB67 binds these elements as a heterodimer with the 9-cis-retinoic acid receptor, RXR. However, MB67 does not bind or activate other retinoic acid response elements with alternative hexamer arrangements or any of several other wild-type and synthetic hormone response elements examined. The transactivation of retinoic acid response elements by MB67 is weaker than that conferred by the retinoic acid receptors but does not require the presence of all-trans retinoic acid, 9-cis-retinoic acid, or any exogenously added ligand. We propose that MB67 plays an important role in the complex network of proteins that govern response to retinoic acid and its metabolites.The nuclear hormone receptor superfamily is a large group of related transcription factors which includes members that bind a diverse array of ligands, including steroids, thyroid hormone (T3), all-trans retinoic acid (RA), 9-cis-retinoic acid (9-cis-RA), and vitamin D (reviewed in references 4,8,19,23,35). In mammals, approximately a dozen genes encode these conventional receptors. An even larger number of genes encode proteins known as orphan receptors (recently compiled in references 1 and 32). These orphans are structurally and functionally related to the conventional receptors but do not bind known ligands.The biological roles of the orphans are generally unknown. Some information is available for a limited number which were initially characterized prior to their identification as superfamily members. HNF-4, for example, was originally identified as a liver-specific basic transcription factor, with binding sites in several genes (59). Similarly, SF-I was identified as a factor associated with activation of expression of several steroidogenic enzymes (31). However, the majority of the orphans were isolated simply by cross-hybridization with probes derived from conventional receptors, and their functions remain largely undefined. By analogy with the conventional receptors, it has generally been thought that most of the orphans will eventually be demonstrated to be ligand-dependent transcriptional activators. However, recent results demonstrate that several, including 30,59), , and NGFI-B/Nur77 (13,48,70)