Brain-type fatty acid-binding protein (B-FABP) belongs to a family of intracellular lipid-binding proteins. B-FABP exhibits a binding affinity to long-chain fatty acids (FAs) whose effects on brain functions including development, emotion, learning and memory have been proposed. B-FABP is localized in the ventricular germinal cells in embryonic brain and astrocytes in developing and mature brain of rodents. In the present study we generated the mouse harboring a null mutation in the B-FABP gene and studied its phenotype. B-FABP mutant mice exhibited the enhanced anxiety and increased fear memory as well as the decreased content of docosahexaenoic acid (DHA) in their brain during the neonatal period without detection of any histological changes in the brain. In the adult brain, B-FABP was localized more numerously to the astrocytes in the amygdala and septal area than to those in the hippocampal area. Analysis of FA content in the amygdala of adult brain revealed that arachidonic and palmitic acids increased significantly in the mutant mice compared with wild-type. Furthermore, the response of N-methyl-d-aspartate receptor-mediated current to DHA in isolated neurons from B-FABP mutant brain was significantly decreased compared with that of wild-type, while no significant differences were detected in behavioral responses related to the spatial learning/memory or in the hippocampal long-term potentiation. These data indicate that B-FABP is crucially involved in the fear memory and anxiety through its binding with FAs and/or its own direct effects on pertinent metabolism/signaling of FAs.

Heart fatty acid binding protein (H-FABP) is expressed in neurons, but its role in brain fatty acid incorporation and metabolism is poorly defined. We examined the effect of H-FABP gene ablation on brain incorporation of arachidonic ([1-(14)C]20:4n-6) or palmitic ([1-(14)C]16:0) acid in vivo. Analysis of brain mRNA confirmed gene ablation and demonstrated no compensatory changes in the levels of other FABP mRNA in the gene-ablated mice. In brains from H-FABP gene-ablated mice, the incorporation coefficient for [1-(14)C]20:4n-6 was reduced 24%, while that for [1-(14)C]16:0 was unaffected. Within the organic and aqueous fractions, significantly more [1-(14)C]20:4n-6 was distributed into the aqueous fraction, suggesting a disruption in the metabolic targeting of 20:4n-6 in these mice. There was less incorporation of [1-(14)C]20:4n-6 into total phospholipids and a marked reduction (51%) in the level of incorporation into the choline glycerophospholipids (ChoGpl). Because FABP can influence steady-state lipid mass, brain individual lipid masses were measured. The brain total phospholipid mass was reduced 17% by gene ablation, ascribed to a 27% and 32% reduction in the masses of ChoGpl and sphingomyelin, respectively. Plasmalogen subclass masses were also reduced, suggesting that H-FABP may augment brain plasmalogen synthesis. In gene-ablated mice, the phosphatidylinositol 20:4n-6 level was reduced 25%, while the proportion of total n-6 fatty acids was reduced in the major phospholipid classes. Thus, these results demonstrate for the first time that H-FABP expression influences brain 20:4n-6 uptake and trafficking as well as steady-state brain lipid levels.

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Glucokinase (GK) plays a key role in the regulation of glucose use and glucose-stimulated insulin secretion in pancreatic islet cells. Gene targeting of the IGF-I receptor down-regulated pancreatic islet GK activity. That finding prompted us to examine the potential mechanism that may control GK gene activity using an islet cell line, INS-1, known to express IGF-I receptor. Exposure of these cells to IGF-I induced GK protein expression and activity of the enzyme in a dose-dependent manner. In addition, IGF-I induced activity of a reporter construct containing the GK promoter in parallel with the effect on endogenous GK mRNA levels. The stimulatory effect of IGF-I on GK promoter activity was abrogated by wortmannin and LY294002, specific inhibitors of phosphatidylinositol 3-kinase. Exposure of cells to IGF-I elicited a rapid phosphorylation of Akt and FoxO1, a known target of Akt signaling. Constitutively active Akt stimulates the activity of the GK promoter, and a dominant-negative mutant of Akt or mutagenesis of a FoxO1 response element in the GK promoter abolished the ability of IGF-I to stimulate the promoter activity. Furthermore, cell knockdown of FoxO1 with small interfering RNA disrupted the effect of IGF-I on GK expression. These results demonstrate that the phosphatidylinositol 3-kinase/Akt/FoxO1 pathway contributes to the regulation of GK gene expression in response to IGF-I stimulation.