No abstract

Restless legs syndrome is a neurological disorder characterized by an urgency to move the legs during periods of rest. Data from a variety of sources provide a compelling argument that the amount of iron in the brain is lower in individuals with restless legs syndrome compared with neurologically normal individuals. Moreover, a significant percentage of patients with restless legs syndrome are responsive to intravenous iron therapy. The mechanism underlying the decreased iron concentrations in restless legs syndrome brains is unknown. We hypothesize that the source of the brain iron deficit is at the blood-brain interface. Thus we analysed the expression of iron management proteins in the epithelial cells of the choroid plexus and the brain microvasculature in post-mortem tissues. The choroid plexus, obtained at autopsy, from 18 neurologically normal controls and 14 individuals who had primary restless legs syndrome was subjected to histochemical staining for iron and immunostaining for iron management proteins. Iron and heavy chain ferritin staining was reduced in the epithelial cells of choroid plexus in restless legs syndrome. Divalent metal transporter, ferroportin, transferrin and its receptor were upregulated in the choroid plexus in restless legs syndrome. Microvessels were isolated from the motor cortex of 11 restless legs syndrome and 14 control brains obtained at autopsy and quantitative immunoblot analyses was performed. Expression of heavy chain ferritin, transferrin and its receptor in the microvessels from restless legs syndrome was significantly decreased compared with the controls but divalent metal protein 1, ferroportin, prohepcidin, mitochondrial ferritin and light-chain ferritin remained unchanged. The presence of an iron regulatory protein was demonstrated in the brain microvasculature and the activity of this protein is decreased in restless legs syndrome; a finding similar to our earlier report in neuromelanin cells from the substantia nigra of restless legs syndrome brains. This study reveals that there are alterations in the iron management protein profile in restless legs syndrome compared with controls at the site of blood-brain interface suggesting fundamental differences in brain iron acquisition in individuals with restless legs syndrome. Furthermore, the decrease in transferrin receptor expression in the microvasculature in the presence of relative brain iron deficiency reported in restless legs syndrome brains may underlie the problems associated with brain iron acquisition in restless legs syndrome. The consistent finding of loss of iron regulatory protein activity in restless legs syndrome brain tissue further implicates this protein as a factor in the underlying cause of the iron deficiency in the restless legs syndrome brain. The data herein provide evidence for regulation of iron uptake and storage within brain microvessels that challenge the existing paradigm that the blood-brain barrier is merely a transport system.

Restless legs syndrome may result from a defect in iron regulatory protein 1 in neuromelanin cells that promotes destabilization of the transferrin receptor mRNA, leading to cellular iron deficiency.

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...