Inhibition of HIF prolyl-4-hydroxylases by FG-4497 Reduces Brain Tissue Injury and Edema Formation during Ischemic Stroke

Abstract

Ischemic stroke results in disruption of the blood-brain barrier (BBB), edema formation and neuronal cell loss. Some neuroprotective factors such as vascular endothelial growth factor (VEGF) favor edema formation, while others such as erythropoietin (Epo) can mitigate it. Both factors are controlled by hypoxia inducible transcription factors (HIF) and the activity of prolyl hydroxylase domain proteins (PHD). We hypothesize that activation of the adaptive hypoxic response by inhibition of PHD results in neuroprotection and prevention of vascular leakage. Mice, subjected to cerebral ischemia, were pre- or post-treated with the novel PHD inhibitor FG-4497. Inhibition of PHD activity resulted in HIF-1α stabilization, increased expression of VEGF and Epo, improved outcome from ischemic stroke and reduced edema formation by maintaining BBB integrity. Additional in vitro studies using brain endothelial cells and primary astrocytes confirmed that FG-4497 induces the HIF signaling pathway, leading to increased VEGF and Epo expression. In an in vitro ischemia model, using combined oxygen and glucose deprivation, FG-4497 promoted the survival of neurons. Furthermore, FG-4497 prevented the ischemia-induced rearrangement and gap formation of the tight junction proteins zonula occludens 1 and occludin, both in cultured endothelial cells and in infarcted brain tissue in vivo. These results indicate that FG-4497 has the potential to prevent cerebral ischemic damage by neuroprotection and prevention of vascular leakage.

Neuronal HIF-1α and HIF-2α deficiency improves neuronal survival and sensorimotor function in the early acute phase after ischemic stroke

“…Subsequently, HIF specifically binds to hypoxia response elements (HREs) in the promoters and enhancers of numerous genes followed by recruitment of p300/CBP resulting in enhanced transcription of HIF-responsive genes. 1,[8][9][10][11][12] A growing number of pre-clinical studies in rodents strongly suggests that activation of the HIF signaling pathway prior or shortly after ischemic stroke by application of low-molecular weight hydroxylase inhibitors 5,[13][14][15][16][17][18][19] or brief exposure to mild systemic hypoxia, [20][21][22][23] reduces tissue damage and increases functional recovery from ischemic stroke. However, as these therapeutic strategies unavoidably lead to pleiotropic activation of HIF signaling throughout all cell types of the central nervous system (CNS), it is difficult to draw conclusions about the definite significance of the HIF signaling pathway in neurons and their viability upon ischemia-reperfusion injury.…”

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“…Along this line, we and others demonstrated that small-molecule PHD inhibitors, applied systemically, improve brain tissue damage and functional deficits in rodent models of ischemic stroke [4]. However, we also provided evidence that combined genetic loss of neuronal HIF-1α and HIF-2α in mice attenuates tissue injury in the early acute phase after cerebral ischemia, although it clearly impairs functional recovery at later stages indicating that activation of the HIF system by PHD suppressors can also have adverse effects [8].…”

“…Both mediators are well known to be potent anti-apoptotic factors, which directly support neuronal survival. Accordingly, application of the PHD inhibitor FG-4497 strongly increased cell survival in pure neuronal cultures exposed to ischemic conditions [4]. In addition, neuronal PHD2 deletion resulted in increased expression of HIF-dependent glucose transporters and glycolytic enzymes [2].…”

Identification of autophagy signaling network that contributes to stroke in the ischemic rodent brain via gene expression

“…It is generally considered to be a heterogeneous and multifactorial disorder and caused by both conventional environmental risk factors and genetic factors [6,7] . It can cause acute neuronal death via oxygen and nutrient depletion, and result in disruption of the blood-brain barrier [8] . Acute ischemic stroke resulting from intracranial vessel occlusion is associated with high morbidity and mortality [9] .…”