Ya Ke

Iron misregulation in the brain : a primary cause of neurodegenerative disorders

High iron concentrations in the brains of patients and the discovery of mutations in the genes associated with iron metabolism in the brain suggest that iron misregulation in the brain plays a part in neuronal death in some neurodegenerative disorders, such as Alzheimers, Parkinsons, and Huntingtons diseases and Hallervorden-Spatz syndrome. Iron misregulation in the brain may have genetic and non-genetic causes. The disrupted expression or function of proteins involved in iron metabolism increases the concentration of iron in the brain. Disturbances can happen at any of several stages in iron metabolism (including uptake and release, storage, intracellular metabolism, and regulation). Increased brain iron triggers a cascade of deleterious events that lead to neurodegeneration. An understanding of the process of iron regulation in the brain, the proteins important in this process, and the effects of iron misregulation could help to treat or prevent neurodegenerative disorders.

Therapeutic Deep Brain Stimulation in Parkinsonian Rats Directly Influences Motor Cortex

Much recent discussion about the origin of Parkinsonian symptoms has centered around the idea that they arise with the increase of beta frequency waves in the EEG. This activity may be closely related to an oscillation between subthalamic nucleus (STN) and globus pallidus. Since STN is the target of deep brain stimulation, it had been assumed that its action is on the nucleus itself. By means of simultaneous recordings of the firing activities from populations of neurons and the local field potentials in the motor cortex of freely moving Parkinsonian rats, this study casts doubt on this assumption. Instead, we found evidence that the corrective action is upon the cortex, where stochastic antidromic spikes originating from the STN directly modify the firing probability of the corticofugal projection neurons, destroy the dominance of beta rhythm, and thus restore motor control to the subjects, be they patients or rodents.

Lipopolysaccharide induces a significant increase in expression of iron regulatory hormone hepcidin in the cortex and substantia nigra in rat brain

Hepcidin plays an essential role in maintaining normal iron homeostasis outside the brain. This recently discovered iron regulation hormone is predominantly expressed in the liver, and regulated by iron and hypoxia. As an antimicrobial peptide, this hormone is also elevated during infections and inflammation. In this study we investigated the expression of hepcidin mRNA and protein in different brain regions, including the cortex, hippocampus, striatum, and substantia nigra, and the effects of lipopolysaccharide (LPS) on the expression of hepcidin using quantitative real-time RT-PCR and immunofluorescence analysis. Our data provided further evidence for the existence of hepcidin in all the regions we examined. We also demonstrated for the first time that LPS administration by iv injection can regulate the expression of hepcidin mRNA and protein not only in peripheral organs such as the liver, but also in the brain. LPS induced a significant increase in the expression of hepcidin mRNA and protein in the cortex and substantia nigra, but not in the hippocampus and striatum, indicating a regionally specific regulation of LPS on hepcidin in the brain. The relevant mechanisms and the functions of hepcidin in the brain remain to be elucidated.

Neuroprotective effect of ligustilide against ischaemia-reperfusion injury via up-regulation of erythropoietin and down-regulation of RTP801

BACKGROUND AND PURPOSE Ligustilide, the main lipophilic component of Danggui, has been reported to protect the brain against ischaemic injury. However, the mechanisms are unknown. Here, we investigated the roles of erythropoietin (EPO) and the stress‐induced protein RTP801 in neuroprotection provided by ligustilide against ischaemia‐reperfusion (I/R) damage to the brain.

L-DOPA Neurotoxicity Is Mediated by Up-Regulation of DMT1−IRE Expression

Background The mechanisms underlying neurotoxicity caused by L-DOPA are not yet completely known. Based on recent findings, we speculated that the increased expression of divalent metal transporter 1 without iron-response element (DMT1−IRE) induced by L-DOPA might play a critical role in the development of L-DOPA neurotoxicity. To test this hypothesis, we investigated the effects of astrocyte-conditioned medium (ACM) and siRNA DMT-IRE on L-DOPA neurotoxicity in cortical neurons. Methods and Findings We demonstrated that neurons treated with L-DOPA have a significant dose-dependent decrease in neuronal viability (MTT Assay) and increase in iron content (using a graphite furnace atomic absorption spectrophotometer), DMT1−IRE expression (Western blot analysis) and ferrous iron (55Fe(II)) uptake. Neurons incubated in ACM with or without L-DOPA had no significant differences in their morphology, Hoechst-33342 staining or viability. Also, ACM significantly inhibited the effects of L-DOPA on neuronal iron content as well as DMT1−IRE expression. In addition, we demonstrated that infection of neurons with siRNA DMT-IRE led to a significant decrease in DMT1−IRE expression as well as L-DOPA neurotoxicity. Conclusion The up-regulation of DMT1−IRE and the increase in DMT1−IRE-mediated iron influx play a key role in L-DOPA neurotoxicity in cortical neurons.

Brain-derived neurotrophic factor rescues and prevents chronic intermittent hypoxia-induced impairment of hippocampal long-term synaptic plasticity

Obstructive sleep apnea (OSA) is a common sleep and breathing disorder characterized by repeated episodes of hypoxemia. OSA causes neurocognitive deficits including perception and memory impairment but the underlying mechanisms are unknown. Here we show that in a mouse model of OSA, chronic intermittent hypoxia treatment impairs both early- and late-phase long-term potentiation (LTP) in the hippocampus. In intermittent hypoxia-treated mice the excitability of CA1 neurons was reduced and hippocampal brain-derived neurotrophic factor (BDNF) was down-regulated. We further showed that exogenous application of BDNF restored the magnitude of LTP in hippocampal slices from hypoxia-treated mice. In addition, microinjection of BDNF into the brain of the hypoxic mice prevented the impairment in LTP. These data suggest that intermittent hypoxia impairs hippocampal neuronal excitability and reduces the expression of BDNF leading to deficits in LTP and memory formation. Thus, BDNF level may be a novel therapeutic target for alleviating OSA-induced neurocognitive deficits.

Reducing iron in the brain: a novel pharmacologic mechanism of huperzine A in the treatment of Alzheimer's disease.

Huperzine A (HupA), a natural inhibitor of acetylcholinesterase derived from a plant, is a licensed anti-Alzheimers disease (AD) drug in China and a nutraceutical in the United States. In addition to acting as an acetylcholinesterase inhibitor, HupA possesses neuroprotective properties. However, the relevant mechanism is unknown. Here, we showed that the neuroprotective effect of HupA was derived from a novel action on brain iron regulation. HupA treatment reduced insoluble and soluble beta amyloid levels, ameliorated amyloid plaques formation, and hyperphosphorylated tau in the cortex and hippocampus of APPswe/PS1dE9 transgenic AD mice. Also, HupA decreased beta amyloid oligomers and amyloid precursor protein levels, and increased A Disintegrin And Metalloprotease Domain 10 (ADAM10) expression in these treated AD mice. However, these beneficial effects of HupA were largely abolished by feeding the animals with a high iron diet. In parallel, we found that HupA decreased iron content in the brain and demonstrated that HupA also has a role to reduce the expression of transferrin-receptor 1 as well as the transferrin-bound iron uptake in cultured neurons. The findings implied that reducing iron in the brain is a novel mechanism of HupA in the treatment of Alzheimers disease.

Hepcidin directly inhibits transferrin receptor 1 expression in astrocytes via a cyclic AMP-protein kinase a pathway

Hepcidin, an iron‐regulatory hormone, plays a central role in iron homeostasis in peripheral tissues. The widespread distribution of hepcidin in the brain implies that the hormone may be essential for brain iron homeostasis. Here, we investigated the effects of hepcidin on the expression of iron uptake proteins, including transferrin receptor 1 (TfR1) and divalent metal transporter1 (DMT1) and the release protein ferroportin1 (Fpn1) in the cultured astrocytes. The effects of hepcidin on iron uptake, including transferrin‐bound iron (Tf‐Fe) and non‐transferrin‐bound iron (NTBI), and iron release were also studied. Our results demonstrated that astrocytes, when treated with hepcidin peptide or infected with hepcidin expression adenovirus (ad‐hepcidin), showed a significant ability in reducing iron uptake (both Tf‐Fe and NTBI), and iron release, which were accompanied by decreased expressions of TfR1, DMT1, and Fpn1. Moreover, we found that the effect of hepcidin in reducing TfR1 expression, which is dependent on the cyclic AMP–protein kinase A pathway, was the primary and dominant event. In conclusion, our results demonstrated that hepcidin controlled iron uptake and release by regulating expression of iron transport proteins. The findings also implied the existence of a novel hepcidin‐receptor on the membrane of astrocytes.

The iron regulatory hormone hepcidin reduces ferroportin 1 content and iron release in H9C2 cardiomyocytes

Iron plays a key pathophysiological role in a number of cardiac diseases. Studies on the mechanisms of heart iron homeostasis are therefore crucial for understanding the causes of excessive heart iron. In addition to iron uptake, cellular iron balance in the heart also depends on iron export. We provided evidence for the existence of iron exporter ferroportin 1 (Fpn1) in the heart in a recent study. The presence of hepcidin, a recently discovered iron regulatory hormone, was also confirmed in the heart recently. Based on these findings and the inhibiting role of hepcidin on Fpn1 in other tissues, we speculated that hepcidin might be able to bind with, internalize and degrade Fpn1 and then decrease iron export in heart cells, leading to an abnormal increase in heart iron and iron mediated cell injury. We therefore investigated the effects of hepcidin on the contents of Fpn1 and iron release in H9C2 cardiomyocyte cell line. We demonstrated that hepcidin has the ability to reduce Fpn1 content as well as iron release in this cell. The similar regulation patterns of hepcidin on the Fpn1 and iron release suggested that the decreased iron release resulted from the decreased content of Fpn1 induced by hepcidin. We also found that hepcidin has no significant effects on ceruloplasmin (CP) and hephaestin (Heph)--two proteins required for iron release from mammalian cells. The data imply that Fpn1, rather than Heph and CP, is the limited factor in the regulation of iron release from heart cells under physiological conditions.

Purity, cell viability, expression of GFAP and bystin in astrocytes cultured by different procedures

Primary astrocyte cultures are the most commonly used in vitro model for neurobiological studies. We speculated that different protocols might induce differences not only in the percentage of astrocytes but also in their biological characteristics. In this study, we investigated the effects of four major protocols on the purity of astrocytes, cell viability, expression of glial fibrillary acidic protein (GFAP) and bystin of cultured astrocytes using MTT assay, immunocytochemical staining, and Western blot analysis. We demonstrated that the purity of astrocytes (98.9%) generated by the subculture (SC) procedure is significantly higher than those generated by primary culture (PC), shaken once culture (SK‐1) or shaken twice culture (SK‐2). We also showed that expressions of GFAP and bystin in astrocytes that are purified by the SK‐2 or SK‐1 procedures are significantly higher than those in astrocytes prepared by PC or SC. In addition, astrocytes cultured by SK‐2 or SK‐1 have a higher level of cell viabilities at most time points after ischemia compared with astrocytes cultured by PC or SC. These suggested that physical stimulation induced by “shaken” or culture operation might be able to activate astrocytes and implied that different procedures induce differences not only in the purity but also in the biological characteristics of astrocytes, such as the percentage of activated astrocytes, GFAP, and bystin expressions and responses to ischemia. A more detailed analysis about the effect of “culture protocol factor” on the biological characteristics of astrocytes is absolutely needed. J. Cell. Biochem. 109: 30–37, 2010.