Characterization and Distribution of Transferrin Receptors in the Rat Brain

Abstract

Transferrin receptors were characterized with 125I-ferrotransferrin on membrane fractions prepared from the rodent forebrain. The distribution of transferrin receptors in the rat brain was investigated further by in vitro autoradiography. Saturation binding analysis revealed an apparent single class of sites with a dissociation constant of 2 nM and a binding site density of 15 pmol/g. The Hill coefficient derived from these data was 1.05, indicating the absence of cooperativity and that 125I-ferrotransferrin binds to a single class of sites. Estimates of the kinetically determined KD for forebrain membranes were within the 2-4 nM range, in agreement with the equilibrium measurements. Apotransferrin and ferrotransferrin competitively displaced the binding of 125I-ferrotransferrin, while ferritin, albumin, and cytochrome c failed to compete for the binding site. Ceruloplasmin, the copper transport protein, was a weak inhibitor of 125I-ferrotransferrin binding. Autoradiographic localization studies demonstrate a heterogeneous distribution of transferrin receptors in the rat brain. Transferrin receptor densities were markedly elevated over the cerebral cortex and the hippocampus. Moderate to high 125I-ferrotransferrin binding was also apparent throughout areas involved in motor functions, including the caudate-putamen, the nucleus accumbens, the substantia nigra, the red nucleus, and the cerebellum.

Antisense imaging of gene expression in the brain in vivo

“…Transport through both of these membranes is required because the target of the antisense imaging agent, the luciferase mRNA, is localized in the cytoplasm of the tumor cells. The TfR is expressed on brain cells (15) and on C6 glioma cells (13), and the data in Fig. 4A show the increased uptake of the PNA conjugate by C6 cells.…”

Noninvasive gene targeting to the brain

“…The uptake into brain cells occurs because the targeting moiety mediates both the transcytosis through the BBB and the endocytosis of the complex into brain cells. These pathways are accessed owing to expression of the TfR both on the brain capillary endothelium (31), which forms the BBB in vivo, and on the plasma membrane of brain cells (32). The liposomes may fuse with endosomal membranes within brain cells, which allows for extrusion of the plasmid DNA into the cytosolic compartment, where the DNA can then move into the nuclear space.…”

Blood-brain barrier biology and methodology

“…A vasoactive intestinal peptide (VIP) pharmaceutical has been delivered to brain for purposes of enhancing cerebral blood¯ow (Wu and Pardridge, 1996). A brain derived neurotrophic factor (BDNF) pharmaceutical has been delivered across the BBB with this system for neuroprotection of hippocampal CA1 neurons following transient forebrain ischemia (Wu and Pardridge, 1999) Subsequent to transport through the BBB, the conjugate may undergo receptor-mediated endocytosis into brain cells expressing the TfR or HIR, which are ubiquitously expressed throughout the brain (Mash et al, 1990). Following endocytosis into brain cells, the conjugate is transferred to the lysosomal compartment and is degraded.…”