Expression of transferrin binding protein in the capillaries of the brain in the developing chick embryo

Cobalt accumulation and iron-regulatory protein profile expression in immature mouse brain after perinatal exposure to cobalt chloride

Developing brain is very sensitive to the influence of environmental factors during gestation and the neonatal period. The aim of the study is to assess cobalt and iron accumulation in the brain as well as changes in the expression of iron-regulatory proteins transferrin receptor 1, hepcidin, and ferroportin in suckling mice. Perinatal exposure to cobalt chloride increased significantly cobalt content in brain tissue homogenates of 18-day-old (d18) and 25-day-old (d25) mice inducing alterations in brain iron homeostasis. Higher degree of transferrin receptor 1 expression was demonstrated in cobalt chloride-exposed mice with no substantial changes between d18 and d25 mice. A weak ferroportin expression was found in 18-day-old control and cobalt-treated mouse brain. Cobalt exposure of d25 mice resulted in increased ferroportin expression in brain compared to the untreated age-matched control group. Hepcidin level in cobalt-exposed groups was decreased in d18 mice and slightly increased in d25 mice. The obtained data contribute for the better understanding of metal toxicity impact on iron homeostasis in the developing brain with further possible implications in neurodegeneration.

Transient expression of iron transport proteins in the capillary of the developing rat brain

Iron is essential for normal brain function and its uptake in the developing rat brain peaks during the first two weeks after birth, prior to the formation of the blood–brain barrier (BBB). The first step of iron transport from the blood to the brain is transferrin receptor (TfR)-mediated endocytosis in the capillary endothelial cells. However, the subsequent step from the endothelium into interstitium has not been fully described. The goal of this study was to examine the expression of iron transport proteins by immunodetection and RT–PCR in the developing rat brain. Tf and TfR are transiently expressed in perivascular NG2+ cells of the capillary wall during the early postnatal weeks in the rat brain. However, MTP-1 and hephaestin were expressed in endothelial cells, but not in the NG2+ perivascular cells. Immunoblot analysis for these iron transfer proteins in the developing brain generally confirmed the immunochemical findings. Furthermore, the expression of Tf and TfR in the blood vessels precedes its expression in oligodendrocytes, the main iron-storing cells in the vertebrate brain. RT–PCR analysis for the primary culture of endothelial cells and pericytes revealed that Tf and TfR were highly expressed in the pericytes while MTP-1 and hephaestin were expressed in the endothelial cells. The specific expression of Tf and TfR in brain perivascular cells and MTP-1 and hephaestin in endothelial cells suggest the possibility that trafficking of elemental iron through perivascular cells may be instrumental in the distribution of iron in the developing central nervous system.

Cerebral microbleeds in the elderly: a pathological analysis

BACKGROUND AND PURPOSE

Cerebral microbleeds in the elderly are routinely identified by brain MRI. The purpose of this study was to better characterize the pathological basis of microbleeds.

METHODS

We studied postmortem brain specimens of 33 individuals with no clinical history of stroke and with an age range of 71 to 105 years. Cerebral microbleeds were identified by presence of hemosiderin (iron), identified by routine histochemistry and Prussian blue stain. Cellular localization of iron (in macrophages and pericytes) was studied by immunohistochemistry for smooth muscle actin, CD68, and, in selected cases, electron microscopy. Presence of β-amyloid was analyzed using immunohistochemistry for epitope 6E10.

RESULTS

Cerebral microbleeds were present in 22 cases and occurred at capillary, small artery, and arteriolar levels. Presence of microbleeds occurred independent of amyloid deposition at site of microbleeds. Although most subjects had hypertension, microbleeds were present with and without hypertension. Putamen was the site of microbleeds in all but 1 case; 1 microbleed was in subcortical white matter of occipital lobe. Most capillary microbleeds involved macrophages, but the 2 microbleeds studied by electron microscopy demonstrated pericyte involvement.

CONCLUSIONS

These findings indicate that cerebral microbleeds are common in elderly brain and can occur at the capillary level.