Reduced blood‐brain barrier expression of fatty acid‐binding protein 5 is associated with increased vulnerability of APP/PS1 mice to cognitive deficits from low omega‐3 fatty acid diets

Purkinje cell degeneration (pcd) was first identified in a spontaneous mouse mutant showing cerebellar ataxia. In addition to cerebellar Purkinje cells (PCs), retinal photoreceptors, mitral cells in the olfactory bulb, and a discrete subpopulation of thalamic neurons also degenerate in the mutant brains. The gene responsible for the pcd mutant is Nna1, also known as ATP/GTP binding protein 1 or cytosolic carboxypeptidase-like 1, which encodes a zinc carboxypeptidase protein. To investigate pathogenesis of the pcd mutation in detail, we generated a conditional Nna1 allele targeting the carboxypeptidase domain at C-terminus. After Cre recombination and heterozygous crossing, we generated Nna1 knockout (KO) mice and found that the Nna1 KO mice began to show cerebellar ataxia at postnatal day 20 (P20). Most PCs degenerated until 4-week-old, except lobule X. Activated microglia and astrocytes were also observed in the Nna1 KO cerebellum. In the mutant brain, the Nna1 mRNA level was dramatically reduced, suggesting that nonsense-mediated mRNA decay occurs in it. Since the Nna1 protein acts as a de-glutamatase on the C-terminus of α-tubulin and β-tubulin, increased polyglutamylated tubulin was detected in the Nna1 KO cerebellum. In addition, the endoplasmic reticulum stress marker, C/EBP homologous protein (CHOP), was up-regulated in the mutant PCs. We report the generation of a functional Nna1 conditional allele and possible mechanisms of PC death in the Nna1 KO in the cerebellum. OPEN PRACTICES: This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/.

Section: Methodsmentioning

confidence: 97%

Deletion of exons encoding carboxypeptidase domain of Nna1 results in Purkinje cell degeneration (pcd) phenotype

Zhou

Hossain

Yamazaki

et al. 2018

“…, ), observations of reduced BBB trafficking of DHA in mouse models of AD (Calon ; Pan et al . ) suggest that reversing BBB dysfunction associated with DHA trafficking in AD could hold therapeutic potential. We have demonstrated that the levels of a key BBB trafficking protein FABP5 are diminished in a mouse model of AD (Pan et al .…”

Section: Discussionmentioning

confidence: 99%

“…We have demonstrated that the levels of a key BBB trafficking protein FABP5 are diminished in a mouse model of AD (Pan et al . ) and postulate that approaches aimed at increasing the levels of FABP5 could restore brain DHA levels in AD. As DHA itself can affect PPAR activation and PPAR activation may be involved in regulation of FABP5 (Armstrong et al .…”

Section: Discussionmentioning

confidence: 99%

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Dietary docosahexaenoic acid supplementation enhances expression of fatty acid‐binding protein 5 at the blood–brain barrier and brain docosahexaenoic acid levels

Pan

Morris

Scanlon

et al. 2018

Self Cite

The cytoplasmic trafficking of docosahexaenoic acid (DHA), a cognitively beneficial fatty acid, across the blood-brain barrier (BBB) is governed by fatty acid-binding protein 5 (FABP5). Lower levels of brain DHA have been observed in Alzheimer's disease (AD), which is associated with diminished BBB expression of FABP5. Therefore, up-regulating FABP5 expression at the BBB may be a novel approach for enhancing BBB transport of DHA in AD. DHA supplementation has been shown to be beneficial in various mouse models of AD, and therefore, the aim of this study was to determine whether DHA has the potential to up-regulate the BBB expression of FABP5, thereby enhancing its own uptake into the brain. Treating human brain microvascular brain endothelial (hCMEC/D3) cells with the maximum tolerable concentration of DHA (12.5 μM) for 72 h resulted in a 1.4-fold increase in FABP5 protein expression. Associated with this was increased expression of fatty acid transport proteins 1 and 4. To study the impact of dietary DHA supplementation, 6- to 8-week-old C57BL/6 mice were fed with a control diet or a DHA-enriched diet for 21 days. Brain microvascular FABP5 protein expression was up-regulated 1.7-fold in mice fed the DHA-enriched diet, and this was associated with increased brain DHA levels (1.3-fold). Despite an increase in brain DHA levels, reduced BBB transport of C-DHA was observed over a 1 min perfusion, possibly as a result of competitive binding to FABP5 between dietary DHA and C-DHA. This study has demonstrated that DHA can increase BBB expression of FABP5, as well as fatty acid transporters, overall increasing brain DHA levels.

“…Our earlier metabolomics study showed that the extracellular concentration of endogenous unesterified DHA is higher than the intracellular concentration at the steady state in FATP1‐overexpressing human embryonic kidney 293 cells (Ochiai et al ). Furthermore, the protein amount of FATP1 in brain homogenate of AD model mice (amyloid precursor protein (APP)/PS1 mice) is decreased (Pan et al ). On the basis of these reports, we hypothesized that the expression level of FATP1 is decreased at the abluminal membrane of brain capillary endothelial cells by the accumulation of Aβ, resulting in a decrease in transport of unesterified DHA from brain capillary endothelial cells into the brain via FATP1.…”

mentioning

confidence: 99%

Amyloid beta_25‐35 impairs docosahexaenoic acid efflux by down‐regulating fatty acid transport protein 1 (FATP1/SLC27A1) protein expression in human brain capillary endothelial cells

Ochiai

Uchida

Tachikawa

2019

Decreased levels of docosahexaenoic acid (DHA), an endogenous neuroprotective compound, in the brain are associated with the development of Alzheimer’s disease (AD). We previously showed that DHA is a substrate of fatty acid transport protein 1 (FATP1/SLC27A1), and FATP1 is localized at the abluminal membrane of brain capillary endothelial cells. We hypothesized that amyloid β (Aβ) decreases FATP1‐mediated cellular efflux (i.e. supply to the brain) of DHA at the blood–brain barrier (BBB). Here, we tested this hypothesis using a human cerebral microvascular endothelial cell line, human cerebral microvessel endothelial cells (hCMEC/D3), as a BBB model. The efflux of DHA‐d5 by hCMEC/D3 cells increased time‐dependently up to 3 min. Knock‐down of FATP1 with specific siRNA indicated that FATP1‐mediated efflux accounts for 47.0% of this DHA‐d5 efflux. In hCMEC/D3 cells treated with Aβ25–35 (10 μM/24 h), which we employed as an in vitro model of the BBB in AD, FATP1 protein expression in the plasma membrane was decreased by 96.0%, which was greater than the decrease in the whole‐cell lysate, and the DHA‐d5 efflux was decreased by 68.3%. Of this 68.3% decrease, 45.1% (47.0 × 0.96) is accounted for by the decrease in FATP1‐mediated efflux and the remaining 23.2% is presumably mediated by other mechanism(s). Thus, we have established for the first time that FATP1 is a major contributor to DHA efflux from human brain capillary endothelial cells, and its efflux activity at the abluminal membrane of the cells is blocked by Aβ. This may explain the decreased DHA level in the brain of AD patients. Open Science Badges This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/.