The Human Brain GLUT1 Glucose Transporter: Ultrastructural Localization to the Blood—Brain Barrier Endothelia

Abstract

Immunogold electron microscopy was used to examine human brain resections to localize the GLUT1 glucose transporter. The tissue examined was obtained from a patient undergoing surgery for treatment of seizures, and the capillary profiles examined had characteristics identical to those described previously for active, epileptogenic sites (confirmed by EEG analyses). A rabbit polyclonal antiserum to the full-length human erythrocyte glucose transporter (GLUT1) was labeled with 10-nm gold particle-secondary antibody conjugates and localized immunoreactive GLUT1 molecules in human brain capillary endothelia, with < 0.25% of the particles beyond the capillary profile. Erythrocyte membranes were also highly immunoreactive, whereas macrophage membranes were GLUT1-negative. The number of immunoreactive sites per capillary profile was observed to be 10-fold greater in humans than in previous studies of rat and rabbit brain capillaries. In addition, half of the total number of immunoreactive gold particles were localized to the luminal capillary membrane. We suggest that the blood-brain barrier GLUT1 glucose transporter is up-regulated in seizures, and this elevated transporter activity is characterized by increased GLUT1 transporters, particularly on the luminal capillary membranes. In addition, acute modulation of glucose transporter activity is presumed to involve translocation of GLUT1 from cytoplasmic to luminal membrane sites, demonstrable with quantitative immunogold electron microscopy.

Functional Studies of Threonine 310 Mutations in Glut1

“…Both influx and efflux of Glut1 are required for the transport of blood glucose across the BBB into brain cells (2,3,37,38). We also observed a significant decrease of the zero-trans efflux in the T310I mutant Glut1 to ϳ3% of the wild-type Glut1 activity (Fig.…”

“…It passes from the blood through the capillary endothelial cells of the BBB, traversing the luminal membrane, cytoplasm and abluminal membrane to the brain extracellular pool. An asymmetric distribution of Glut1 on the luminal and abluminal endothelial membranes has been shown by immunogold electron microscopy in human, rabbit, rat, squirrel, and monkey (2)(3)(4). The GLUT1 gene is ϳ35 kb long containing 10 exons and 9 introns and is mapped to the short arm of chromosome 1 (1p35-p31.3).…”

HTLV-1 tropism and envelope receptor

“…Thus, other tissues where GLUT1 is expressed include the endothelial bloodbrain barrier, notably the luminal membrane (Cornford et al, 1994), and various cell types of the eye, including the ganglion cell layer of the retina, the endothelium lining the canal of Schlemm, the corneal endothelium and the basal cells of the corneal epithelium (Kumagai et al, 1994). It will be important to explore whether this diverse expression of GLUT1 in the eye is related with the development of HTLV-associated uveitis (Mochizuki et al, 1996).…”

The Blood–Brain Barrier

“…Slc2a1, also called glut1, has been largely studied for its role in providing the CNS with glucose. Expression of this transporter is highly enriched in CNS ECs compared with ECs in nonneural tissues, and it facilitates the transport of glucose down its concentration gradient from the blood into the brain (Cornford et al 1994). In humans, Glut1 deficiency leads to an epileptic syndrome that is treated by being fed a highketone diet (De Vivo et al 1991, 2002.…”