Hypoxia-inducible Factor Prolyl 4-Hydroxylase Inhibition

Abstract

Hypoxia-inducible factor (HIF) prolyl 4-hydroxylases are a family of iron-and 2-oxoglutarate-dependent dioxygenases that negatively regulate the stability of several proteins that have established roles in adaptation to hypoxic or oxidative stress. These proteins include the transcriptional activators HIF-1␣ and HIF-2␣. The ability of the inhibitors of HIF prolyl 4-hydroxylases to stabilize proteins involved in adaptation in neurons and to prevent neuronal injury remains unclear. We reported that structurally diverse low molecular weight or peptide inhibitors of the HIF prolyl 4-hydroxylases stabilize HIF-1␣ and up-regulate HIF-dependent target genes (e.g. enolase, p21 waf1/cip1 , vascular endothelial growth factor, or erythropoietin) in embryonic cortical neurons in vitro or in adult rat brains in vivo. We also showed that structurally diverse HIF prolyl 4-hydroxylase inhibitors prevent oxidative death in vitro and ischemic injury in vivo. Taken together these findings identified low molecular weight and peptide HIF prolyl 4-hydroxylase inhibitors as novel neurological therapeutics for stroke as well as other diseases associated with oxidative stress.Iron maintains a unique role in physiology via its ability to change readily its oxidation state in response to changes in its local environment. A general simplification of its primary function is that it mediates one-electron redox reactions. This chemical property of iron enables it to act as an essential component in several biological activities, including as a cofactor for enzymes such as tyrosine hydroxylase. Oxygen binding to biomolecules such as hemoglobin and myoglobin is also coordinated by iron. Indeed iron deficiency can lead to a host of disorders, including anemia and restless legs syndrome (1).Paradoxically, the biochemical properties that make iron beneficial in many biological processes appear to be a drawback when the balance between its accumulation/sequestration within cellular compartments and its release is disturbed in favor of iron accumulation (2). Indeed, iron overload is associated with several neurological conditions (3-5). For example, the iron content of nigral Lewy bodies is elevated in patients with Parkinson disease (6 -9). Alzheimer disease has also been found to be associated with an increase in the iron content of senile plaques (10 -15). Accumulation of mitochondrial iron has been shown to play a role in Friedrich ataxia (16,17). Similarly, changes in intracellular free iron levels have been observed in cerebral ischemia (18 -20). Direct evidence that disrupted iron homeostasis contributes to injury rather than simply being caused by it has been obtained by treatment with low molecular weight iron chelators or by overexpression of iron storage proteins. Small molecule iron chelators such as deferoxamine mesylate (DFO) 2 inhibit neuronal injury in rodent models of stroke (21), Parkinson disease (22), and multiple sclerosis (23). Moreover, DFO and some other metal chelators such as clioquinol have been shown to slow the progressi...

Clioquinol, a Cu(II)/Zn(II) Chelator, Inhibits Both Ubiquitination and Asparagine Hydroxylation of Hypoxia-inducible Factor-1α, Leading to Expression of Vascular Endothelial Growth Factor and Erythropoietin in Normoxic Cells

“…Activation of HIF-1␣ also promotes the survival and progression of various cancers (29,30). In contrast, it has beneficial effects on ischemic injury to the heart and brain, suggesting that a low molecular weight activa- tor of HIF-1␣ and its target genes could provide a novel treatment for stroke and myocardial infarction (31,32). The beneficial effects of HIF-1 are mostly mediated by its target genes, the most prominent of which are EPO and VEGF, which are considered major mediators of the protective effect of hypoxic preconditioning (33)(34)(35)(36).…”

Inhibition of Prolyl Hydroxylase Protects against 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced Neurotoxicity

“…Prolyl hydroxylases are iron-dependent enzymes that reduce levels of HIFs via their ability to hydroxylate these proteins, marking them for subsequent degradation by the ubiquitinproteasome system. Reduction in HIF signaling pathways by PHDs results in decreased transcription of several genes whose protein products have been shown to be protective against either oxygen depletion or oxidative stress within the brain (10,44,45). Because PHDs require the presence of iron, it is possible that iron chelation therapy is in part protective against MPTP neurotoxicity by resulting in decreased PHD activity, which can contribute to the induction of protective HIF-dependent genes including those involved in cellular iron regulation and protection against oxidative stress and mitochondrial dysfunction.…”

“…PHD inhibitors have been demonstrated to prevent oxidative cell death and ischemic injury via HIF pathway activation (10). More recently, it has been shown that inactivation of HIF-1␣ in specific cortical and striatal neurons exacerbated tissue damage in a mouse model of ischemia (11).…”

“…DHB is a low molecular weight inhibitor of PHD that displaces 2-oxoglutarate or ascorbate, co-factors required for PHD activity (17), and has been shown to reduce infarct volume induced by middle cerebral artery occlusion (10). Tyrosine hydroxylase (TH) is the rate-limiting enzyme involved in DA synthesis and positive staining of the cell for TH distinguishes DAergic neurons from other cellular populations.…”

Roles of Hypoxia Response in Retinal Development and Pathophysiology

“…11,12 Furthermore, it was reported that a hypoxic environment and the function of HIFs are important for the maintenance of neuronal undifferentiation and proliferation, 13,14 and that hypoxic preconditioning or pharmacological HIF activation may suppress pathological phenotypes of experimental retinal degeneration and cerebral infarction. 15,16 Based on this background, we hypothesized that constitutive HIF activation may protect the retina from various disease states. Consequently, we undertook the generation of a mouse line that lacks the von Hippel-Lindau gene (Vhl, a negative regulator of HIFs) specifically in the retinal neuron.…”