Ischemic brain damage, including that caused by stroke and trauma, elicits inflammation in the injured areas [
1‐
3]. A number of inflammatory mediators are expressed in the brain in response to ischemia and hypoxia [
1‐
4]. Hypoxia or ischemia stimulates the expression of inflammatory cytokines (IL-1β, TNF-α), chemokines (IL-8, MCP-1/CCL2) and adhesion molecules (ICAM-1) in the brain and in cultured astrocytes and brain endothelial cells [
5‐
10]. These inflammatory mediators play a critical role not only in the initiation and propagation of ischemica/hypoxia-evoked neuroinflammation but also in the resolution of brain damage [
1‐
4]. However, triggers of inflammatory chemokine up-regulation by hypoxia/ischemia in these cells are poorly understood. We have recently shown that hypoxia-stimulated IL-1β expression in astrocytes is mediated by hypoxia-inducible factor-1α (HIF-1α) [
11]. Hypoxia-inducible factor-1 (HIF-1) is a transcription factor that plays a central role in cellular and systemic homeostatic responses to hypoxia [
12‐
14]. HIF-1 is a heterodimeric protein complex consisting of two subunits, the redox-sensitive HIF-1α (120–130 kD), which is unique to HIF-1, and the constitutively expressed HIF-1β (91–94 kD), a common partner for many other transcription factors [
12‐
14]. Both subunits are necessary for DNA binding and activation of HIF-1 target genes [
15,
16]. Several HIF-1α isoforms have been found, including HIF-2α and HIF-3α, both of which have significant homologies to HIF-1α [
13,
14,
17]. Although these HIF-1 isoforms may also contribute to the response to hypoxia, HIF-1α is considered the major regulator of O
2-tension sensitive genes in cells [
12,
13]. Decrease in cellular O
2 tension or the presence of CoCl
2 or desferroxamine leads to elevation of HIF-1α expression, whereas carbon monoxide and nitric oxide inhibit HIF-1 activation [
18‐
20]. HIF-1α is cytosolic and degraded by ubiquitin-proteasome pathway [
21,
22] via binding of von Hippel-Lindau tumor suppressor protein to the oxygen-dependent degradation domain [
23]. Hypoxia induces HIF-1α expression in tissues and cultured cells [
12,
13,
24]. The length of hypoxic stress determines HIF-1α half-life upon reoxygenation. During hypoxia, HIF-1α is stabilized and dimerized with HIF-1β, and the complex is translocated into nucleus where it binds to hypoxia-responsive elements in the promoters or enhancers of the target genes, such as the genes encoding erythropoetin (EPO), glucose transporters, glycolytic enzymes, heme oxygenase-1, inducible nitric oxide synthase, transferin, and vascular endothelial growth factor (VEGF) [
12‐
14,
25,
26]. The consensus DNA sequence for HIF-1 binding in the hypoxia-response element is 5'-[A/G]CGTG-3' flanked with or without a second consensus site 5'-[A/C]ACAG-3' [
12]. Mutations of the consensus sequences result in loss of HIF-1 binding and transcriptional response of the genes to hypoxia [
12].
In vitro exposure to CoCl
2 or iron chelator deferoxamine under normoxic conditions produces a hypoxia-mimetic effect with up-regulation of HIF-1α and target gene expression [
12‐
14,
26]. Cobalt chloride (CoCl
2) increases erythropoetin (EPO) production
in vitro [
27] and
in vivo [
28] under normoxic conditions and was once given to human patients to treat anemia.
Astroglial cells are the most abundant cells in the brain and serve as an important source of inflammatory mediators during the course of neuroinflammation [
1‐
3]. Astrocytes subjected to
in vitro ischemia/hypoxia produce a large amount of chemoattractant MCP-1 which is 30-time higher than that secreted by human brain endothelial cells subjected to the same treatment [
6]. MCP-1 is a potent chemokine and directs the transmigration of blood-borne monocytes/macrophages across the blood-brain barrier (BBB) into the inflammatory sites in the brain [
1‐
3]. Mouse monocyte chemoattractant protein-5 (MCP-5), known as chemokine (C-C motif) ligand 12 (Ccl12) or small inducible cytokine A12 (Scya12), is also a potent monocyte chemokine homologous to human MCP-1 with 66% amino acid identity [
29]. This study shows that HIF-1α is involved in transcriptional activation of MCP-1 and MCP-5 expression stimulated by hypoxia in human and mouse astrocytes, respectively.