Fatty Acid-Binding Protein 5 Facilitates the Blood–Brain Barrier Transport of Docosahexaenoic Acid

Abstract

The brain has a limited ability to synthesize the essential polyunsaturated fatty acid (PUFA) docosahexaenoic acid (DHA) from its omega-3 fatty acid precursors. Therefore, to maintain brain concentrations of this PUFA at physiological levels, plasma-derived DHA must be transported across the blood-brain barrier (BBB). While DHA is able to partition into the luminal membrane of brain endothelial cells, its low aqueous solubility likely limits its cytosolic transfer to the abluminal membrane, necessitating the requirement of an intracellular carrier protein to facilitate trafficking of this PUFA across the BBB. As the intracellular carrier protein fatty acid-binding protein 5 (FABP5) is expressed at the human BBB, the current study assessed the putative role of FABP5 in the brain endothelial cell uptake and BBB transport of DHA in vitro and in vivo, respectively. hFAPB5 was recombinantly expressed and purified from Escherichia coli C41(DE3) cells and the binding affinity of DHA to hFABP5 assessed using isothermal titration calorimetry. The impact of FABP5 siRNA on uptake of (14)C-DHA into immortalized human brain microvascular endothelial (hCMEC/D3) cells was assessed. An in situ transcardiac perfusion method was optimized in C57BL/6 mice and subsequently used to compare the BBB influx rate (Kin) of (14)C-DHA between FABP5-deficient (FABP5(-/-)) and wild-type (FABP5(+/+)) C57BL/6 mice. DHA bound to hFABP5 with an equilibrium dissociation constant of 155 ± 8 nM (mean ± SEM). FABP5 siRNA transfection decreased hCMEC/D3 mRNA and protein expression of FABP5 by 53.2 ± 5.5% and 44.8 ± 13.7%, respectively, which was associated with a 14.1 ± 2.7% reduction in (14)C-DHA cellular uptake. By using optimized conditions for the in situ transcardiac perfusion (a 1 min preperfusion (10 mL/min) followed by perfusion of (14)C-DHA (1 min)), the Kin of (14)C-DHA was 0.04 ± 0.01 mL/g/s. Relative to FABP5(+/+) mice, the Kin of (14)C-DHA decreased 36.7 ± 12.4% in FABP5(-/-) mice. This study demonstrates that FABP5 binds to DHA and is involved in the brain endothelial cell uptake and subsequent BBB transport of DHA, confirming the importance of this cytoplasmic carrier protein in the CNS exposure of this PUFA essential for neuronal function.

Identification of a fatty acid binding protein4-UCP2 axis regulating microglial mediated neuroinflammation

“…Besides FABP4, other FABPs are also expressed in the brain. FABP7 is necessary for brain development, and FABP5 (mal1) is essential in transporting fatty acids across the blood brain barrier (Furuhashi and Hotamisligil, 2008; Pan et al, 2015). Although knocking out FABP5 peripherally results in attenuated diet-induced obesity, the effects are not as robust as in FABP4 knockout models (Hotamisligil and Bernlohr, 2015).…”

Metabolic compartmentalization between astroglia and neurons in physiological and pathophysiological conditions of the neurovascular unit

“…Although the brain levels of soluble fatty acids have not been reported, fatty acids have long been known to be BBB permeable. Neural cells also reportedly express fatty acid‐binding proteins (FABPs) that take up free fatty acids . Long‐chain fatty acids (> 12 carbons) such as palmitic acid (PAL, 16 carbons), a predominant fatty acid in the body, are then metabolized to produce long‐chain fatty acid acyl‐CoA.…”

Lysophosphatidic acid acyltransferase 3 tunes the membrane status of germ cells by incorporating docosahexaenoic acid during spermatogenesis

“…Together with the fact that mammalian sperm possesses a high amount of PUFA, including DHA (19), it is possible that highly fluid and flexible membrane is required for sperm formation and functions. Recent gene knock-out strategies as well as analyses of human genetic disorders have unveiled several important molecules involved in the uptake and trafficking of DHA (20–22); however, the mechanism of how lipid profiles affect the male reproductive system is not well understood.…”