Uptake and transport of high‐density lipoprotein (HDL) and HDL‐associated α‐tocopherol by an in vitro blood–brain barrier model

Abstract

The present study aimed to investigate pathways that contribute to uptake and transcytosis of high-density lipoproteins (HDLs) and HDL-associated a-tocopherol (aTocH) across an in vitro model of the blood-brain barrier (BBB). In primary porcine brain capillary endothelial cells HDL-associated aTocH was taken up in 10-fold excess of HDL holoparticles, indicating efficient selective uptake, a pathway mediated by scavenger receptor class B, type I (SR-BI). SR-BI was present in caveolae of brain capillary endothelial cells and expressed almost exclusively at the apical membrane. Disruption of caveolae with methyl-b-cyclodextrin (CDX) resulted in (mis)sorting of SR-BI to the basolateral membrane. Immunohistochemistry of porcine brain cryosections revealed SR-BI expression on brain capillary endothelial cells and presumably astrocytic endfeet. HDLassociated [14 C]aTocH taken up by brain capillary endothelial cells was recovered in sucrose gradient fractions containing the majority of cellular caveolin-1, the major caveolae-associated protein.During mass transfer studies using aTocH-enriched HDL, approximately 50% of cellular aTocH was recovered with the bulk of cellular caveolin-1 and SR-BI. Efflux experiments revealed that a substantial amount of cell-associated [ 14 C]aTocH could be mobilized into the culture medium. In addition, apical-to-basolateral transport of HDL holoparticles and HDL-associated aTocH was saturable. Results from the present study suggest that part of cerebral apolipoprotein A-I and aTocH originates from plasma HDL transcytosed across the BBB and that caveolae-located SR-BI facilitates selective uptake of HDLassociated aTocH at the BBB.

Lipoprotein Particles Cross the Blood–Brain Barrier inDrosophila

“…The possibility that lipoproteins cross the BBB has been suggested by the presence of lipoprotein receptors on BBB cells, and by the observation that peptides derived from ApoE and ApoB promote transport of linked proteins across the BBB (Balazs et al, 2004;Kreuter et al, 2007;Spencer and Verma, 2007;Candela et al, 2008;Zensi et al, 2009). Nevertheless, there has been no evidence to show that circulating lipoproteins cross the BBB in vivo, or what their function in the brain might be if they did.…”

“…Lipoproteins mediate interorgan transport of nutritional and signaling lipids, and also bear a variety of lipid-linked signaling molecules (Panáková et al, 2005). Vertebrate BBB cells express lipoprotein receptors, and transcytose both LDL and HDL in tissue culture (Dehouck et al, 1997;Balazs et al, 2004). Furthermore, linking peptides derived from ApoE and ApoB to other molecules can promote their transport across the BBB (Spencer and Verma, 2007;Zensi et al, 2009).…”

CLA-1 and its splicing variant CLA-2 mediate bacterial adhesion and cytosolic bacterial invasion in mammalian cells

“…1 and 2). Organs with the highest expression of CLA-1͞SR-BI include the liver, adrenals, ovaries, and testes, whereas a relatively high expression has been demonstrated in intestinal cells, phagocytes, and endothelial cells (3,4). In steroid-producing tissues, such as the adrenals, most of the cholesterol for steroid hormone production is delivered through CLA-1͞SR-BI.…”

Loss of astrocyte cholesterol synthesis disrupts neuronal function and alters whole-body metabolism

“…Cholesterol levels are tightly controlled by sterol regulatory element-binding protein 2 (SREBP2), the major transcription factor regulating cholesterol synthetic genes (2). In contrast to fatty acids, which are in equilibrium with the rest of the body, nearly all brain cholesterol is synthesized in the brain because cholesterol-carrying lipoproteins, with the exception of some very dense HDL, cannot readily cross the blood-brain barrier (3)(4)(5).…”