Hypoxia inducible factor-1: its potential role in cerebral ischemia

Abstract

A divergence in the supply and consumption of oxygen in brain tissue initiates complex cycle of biochemical and molecular events resulting in neuronal death. To overcome such adverse situation, the tissue has to adopt some cellular mechanisms such as induction of various transcription factors, such as hypoxia inducible factor (HIF). It is a transcriptional regulator of oxygen homeostasis and key factor to generate the adaptive responses through upregulation of various target genes involved in the erythropoiesis, angiogenesis as well as glucose metabolism and transport. On the other hand, some studies do suggest that HIF also plays a detrimental role in ischemic reperfusion injury by inducing the pro apoptotic molecules, cytokines such as Nix, BNip3, and IL-20 which cause mitochondrial dysfunction leading to cell death. Hence, modulation of HIF-1 activity seems to provide an innovative therapeutic target to reduce the cellular damage, which arises from ischemic injury. Apart from traditional oxygen dependent HIF regulation, the focus has now shifted toward oxygen independent regulation in cell specific manner through reactive oxygen species involving hypoxia-associated factor, and heat shock protein 90, etc. Therefore, future development of such small molecule regulators for HIF-1 stability and signaling may prove useful to therapeutically target for enhancing recovery and repair in I/R injury.

Fig. 1

A systematic representation of HIF regulation under normoxic and hypoxic conditions. Under normal condition HIF-1α subunit is hydroxylated by PHD and FIH, which makes it susceptible to the binding of pVHL leading to the recruitment of E3 ligase. The HIF-1α subunit is then subjected to ubiquitin dependent proteosomal degradation. Under hypoxia PHDs and FIH inhibit, and stabilize HIF-1, which moves into the nucleus and binds to HIF-1β and this heterodimer binds to HRE and transcribes a number of genes

Fig. 2

A proposed mechanism for regulation of HIF by ROS during cerebral ischemia