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.

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The von Hippel-Lindau (VHL) tumor suppressor functions as a ubiquitin ligase that mediates proteolytic inactivation of hydroxylated α subunits of hypoxia-inducible factor (HIF). Although studies of VHL-defective renal carcinoma cells suggest the existence of other VHL tumor suppressor pathways, dysregulation of the HIF transcriptional cascade has extensive effects that make it difficult to distinguish whether, and to what extent, observed abnormalities in these cells represent effects on pathways that are distinct from HIF. Here, we report on a genetic analysis of HIF-dependent and -independent effects of VHL inactivation by studying gene expression patterns in Caenorhabditis elegans. We show tight conservation of the HIF-1/VHL-1/EGL-9 hydroxylase pathway. However, persisting differential gene expression in hif-1 versus hif-1; vhl-1 double mutant worms clearly distinguished HIF-1–independent effects of VHL-1 inactivation. Genomic clustering, predicted functional similarities, and a common pattern of dysregulation in both vhl-1 worms and a set of mutants (dpy-18, let-268, gon-1, mig-17, and unc-6), with different defects in extracellular matrix formation, suggest that dysregulation of these genes reflects a discrete HIF-1–independent function of VHL-1 that is connected with extracellular matrix function.

Hypoxia inducible factors (HIFs) are α/β heterodimeric transcription factors that direct multiple cellular and systemic responses in response to changes in oxygen availability. The oxygen sensitive signal is generated by a series of iron and 2-oxoglutarate-dependent dioxygenases that catalyze post-translational hydroxylation of specific prolyl and asparaginyl residues in HIFα subunits and thereby promote their destruction and inactivation in the presence of oxygen. In hypoxia, these processes are suppressed allowing HIF to activate a massive transcriptional cascade. Elucidation of these pathways has opened several new fields of cardiovascular research. Here, we review the role of HIF hydroxylase pathways in cardiac development and in cardiovascular control. We also consider the current status, opportunities, and challenges of therapeutic modulation of HIF hydroxylases in the therapy of cardiovascular disease. (Circ Res. 2015;117:65-79.