Brain eicosapentaenoic acid metabolism as a lead for novel therapeutics in major depression.

The results of several meta-analyses suggest that eicosapentaenoic acid (EPA) supplementation is therapeutic in managing the symptoms of major depression. It was previously assumed that because EPA is extremely low in the brain it did not cross the blood-brain barrier and any therapeutic effects it exerted would be via the periphery. However, more recent studies have established that EPA does enter the brain, but is rapidly metabolised following entry. While EPA does not accumulate within the brain, it is present in microglia and homeostatic mechanisms may regulate its esterification to phospholipids that serve important roles in cell signaling. Furthermore, a variety of signaling molecules from EPA have been described in the periphery and they have the potential to exert effects within the brain. If EPA is confirmed to be therapeutic in major depression as a result of adequately powered randomized clinical trials, future research on brain EPA metabolism could lead to the discovery of novel targets for treating or preventing major depression.

Maternal n-3 polyunsaturated fatty acid dietary supply modulates microglia lipid content in the offspring.

The brain is highly enriched in long chain polyunsaturated fatty acids (LC-PUFAs) that are esterified into phospholipids, the major components of cell membranes. They accumulate during the perinatal period when the brain is rapidly developing. Hence, the levels of LC-PUFAs in the brains of the offspring greatly depend on maternal dietary intake. Perinatal n-3 PUFA consumption has been suggested to modulate the activity of microglial cells, the brain's innate immune cells which contribute to the shaping of neuronal network during development. However, the impact of maternal n-3 PUFA intake on microglial lipid composition in the offspring has never been studied. To investigate the impact of maternal dietary n-3 PUFA supply on microglia lipid composition, pregnant mice were fed with n-3 PUFA deficient, n-3 PUFA balanced or n-3 PUFA supplemented diets during gestation and lactation. At weaning, microglia were isolated from the pup's brains to analyze their fatty acid composition and phospholipid class levels. We here report that post-natal microglial cells displayed a distinctive lipid profile as they contained high levels of eicosapentaenoic acid (EPA), more EPA than docosahexaenoic acid (DHA) and large amount of phosphatidylinositol (PI) / phosphatidylserine (PS). Maternal n-3 PUFA supply increased DHA levels and decreased n-6 docosapentaenoic acid (DPA) levels whereas the PI/PS membrane content was inversely correlated to the quantity of PUFAs in the diet. These results raise the possibility of modulating microglial lipid profile and their subsequent activity in the developing brain.

Inhibiting Microglia Expansion Prevents Diet-Induced Hypothalamic and Peripheral Inflammation.

Cell proliferation and neuroinflammation in the adult hypothalamus may contribute to the pathogenesis of obesity. We tested whether the intertwining of these two processes plays a role in the metabolic changes caused by 3 weeks of a high-saturated fat diet (HFD) consumption. Compared with chow-fed mice, HFD-fed mice had a rapid increase in body weight and fat mass and specifically showed an increased number of microglia in the arcuate nucleus (ARC) of the hypothalamus. Microglia expansion required the adequate presence of fats and carbohydrates in the diet because feeding mice a very high-fat, very low-carbohydrate diet did not affect cell proliferation. Blocking HFD-induced cell proliferation by central delivery of the antimitotic drug arabinofuranosyl cytidine (AraC) blunted food intake, body weight gain, and adiposity. AraC treatment completely prevented the increase in number of activated microglia in the ARC, the expression of the proinflammatory cytokine tumor necrosis factor-α in microglia, and the recruitment of the nuclear factor-κB pathway while restoring hypothalamic leptin sensitivity. Central blockade of cell proliferation also normalized circulating levels of the cytokines leptin and interleukin 1ß and decreased peritoneal proinflammatory CD86 immunoreactive macrophage number. These findings suggest that inhibition of diet-dependent microglia expansion hinders body weight gain while preventing central and peripheral inflammatory responses due to caloric overload.

Modulation of brain PUFA content in different experimental models of mice.

The relative amounts of arachidonic acid (AA) and docosahexaenoic acid (DHA) govern the different functions of the brain. Their brain levels depend on structures considered, on fatty acid dietary supply and the age of animals. To have a better overview of the different models available in the literature we here compared the brain fatty acid composition in various mice models (C57BL/6J, CD1, Fat-1, SAMP8 mice) fed with different n-3 PUFA diets (deficient, balanced, enriched) in adults and aged animals. Our results demonstrated that brain AA and DHA content is 1) structure-dependent; 2) strain-specific; 3) differently affected by dietary approaches when compared to genetic model of PUFA modulation; 4) different in n-3 PUFA deficient aged C57BL6/J when compared to SAMP8 mouse model of aging. From these experiments, we highlight the difficulty to compare results obtained in different mouse models, different strains, different brain regions and different ages.

Dietary n-3 PUFAs Deficiency Increases Vulnerability to Inflammation-Induced Spatial Memory Impairment.

Dietary n-3 polyunsaturated fatty acids (PUFAs) are critical components of inflammatory response and memory impairment. However, the mechanisms underlying the sensitizing effects of low n-3 PUFAs in the brain for the development of memory impairment following inflammation are still poorly understood. In this study, we examined how a 2-month n-3 PUFAs deficiency from pre-puberty to adulthood could increase vulnerability to the effect of inflammatory event on spatial memory in mice. Mice were given diets balanced or deficient in n-3 PUFAs for a 2-month period starting at post-natal day 21, followed by a peripheral administration of lipopolysaccharide (LPS), a bacterial endotoxin, at adulthood. We first showed that spatial memory performance was altered after LPS challenge only in n-3 PUFA-deficient mice that displayed lower n-3/n-6 PUFA ratio in the hippocampus. Importantly, long-term depression (LTD), but not long-term potentiation (LTP) was impaired in the hippocampus of LPS-treated n-3 PUFA-deficient mice. Proinflammatory cytokine levels were increased in the plasma of both n-3 PUFA-deficient and n-3 PUFA-balanced mice. However, only n-3 PUFA-balanced mice showed an increase in cytokine expression in the hippocampus in response to LPS. In addition, n-3 PUFA-deficient mice displayed higher glucocorticoid levels in response to LPS as compared with n-3 PUFA-balanced mice. These results indicate a role for n-3 PUFA imbalance in the sensitization of the hippocampal synaptic plasticity to inflammatory stimuli, which is likely to contribute to spatial memory impairment.

Transgenic increase in n-3/n-6 fatty acid ratio protects against cognitive deficits induced by an immune challenge through decrease of neuroinflammation.

Polyunsaturated fatty acids (PUFAs) display immunomodulatory properties in the brain, n-3 PUFAs being able to reduce inflammation whereas n-6 PUFAs are more pro-inflammatory. It has been extensively demonstrated that exposure to a peripheral immune challenge leads to the production and release of inflammatory mediators in the brain in association with cognitive deficits. The question arises whether n-3 PUFA supplementation could downregulate the brain inflammatory response and subsequent cognitive alterations. In this study, we used a genetically modified mouse line carrying the fat-1 gene from the roundworm Caenorhabditis elegans, encoding an n-3 PUFA desaturase that catalyzes conversion of n-6 into n-3 PUFA. Consequently, these mice display endogenously elevated n-3 PUFA tissue contents. Fat-1 mice or wild-type (WT) littermates were injected peripherally with lipopolysaccharide (LPS), a bacterial endotoxin, to induce an inflammatory episode. Our results showed that LPS altered differently the phenotype of microglia and the expression of cytokines and chemokines in Fat-1 and WT mice. In Fat-1 mice, pro-inflammatory factors synthesis was lowered compared with WT mice, whereas anti-inflammatory mechanisms were favored 24 h after LPS treatment. Moreover, LPS injection impaired spatial memory in WT mice, whereas interestingly, the Fat-1 mice showed normal cognitive performances. All together, these data suggest that the central n-3 PUFA increase observed in Fat-1 mice modulated the brain innate immune system activity, leading to the protection of animals against LPS-induced pro-inflammatory cytokine production and subsequent spatial memory alteration.

Nutritional n-3 PUFAs deficiency during perinatal periods alters brain innate immune system and neuronal plasticity-associated genes.

Low dietary intake of the n-3 polyunsaturated fatty acids (PUFAs) is a causative factor of neurodevelopmental disorders. However the mechanisms linking n-3 PUFAs low dietary intake and neurodevelopmental disorders are poorly understood. Microglia, known mainly for their immune function in the injured or infected brain, have recently been demonstrated to play a pivotal role in regulating maturation of neuronal circuits during normal brain development. Disruption of this role during the perinatal period therefore could significantly contribute to psychopathologies with a neurodevelopmental neurodevelopmental component. N-3 PUFAs, essential lipids and key structural components of neuronal membrane phospholipids, are highly incorporated in cell membranes during the gestation and lactation phase. We previously showed that in a context of perinatal n-3 PUFAs deficiency, accretion of these latter is decreased and this is correlated to an alteration of endotoxin-induced inflammatory response. We thus postulated that dietary n-3 PUFAs imbalance alters the activity of microglia in the developing brain, leading to abnormal formation of neuronal networks. We first confirmed that mice fed with a n-3 PUFAs deficient diet displayed decreased n-3 PUFAs levels in the brain at post-natal days (PND)0 and PND21. We then demonstrated that n-3 PUFAs deficiency altered microglia phenotype and motility in the post-natal developing brain. This was paralleled by an increase in pro-inflammatory cytokines expression at PND21 and to modification of neuronal plasticity-related genes expression. Overall, our findings show for the first time that a dietary n-3 PUFAs deficiency from the first day of gestation leads to the development of a pro-inflammatory condition in the central nervous system that may contribute to neurodevelopmental alterations.

Short-term long chain omega3 diet protects from neuroinflammatory processes and memory impairment in aged mice.

Regular consumption of food enriched in omega3 polyunsaturated fatty acids (ω3 PUFAs) has been shown to reduce risk of cognitive decline in elderly, and possibly development of Alzheimer's disease. Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are the most likely active components of ω3-rich PUFAs diets in the brain. We therefore hypothesized that exposing mice to a DHA and EPA enriched diet may reduce neuroinflammation and protect against memory impairment in aged mice. For this purpose, mice were exposed to a control diet throughout life and were further submitted to a diet enriched in EPA and DHA during 2 additional months. Cytokine expression together with a thorough analysis of astrocytes morphology assessed by a 3D reconstruction was measured in the hippocampus of young (3-month-old) and aged (22-month-old) mice. In addition, the effects of EPA and DHA on spatial memory and associated Fos activation in the hippocampus were assessed. We showed that a 2-month EPA/DHA treatment increased these long-chain ω3 PUFAs in the brain, prevented cytokines expression and astrocytes morphology changes in the hippocampus and restored spatial memory deficits and Fos-associated activation in the hippocampus of aged mice. Collectively, these data indicated that diet-induced accumulation of EPA and DHA in the brain protects against neuroinflammation and cognitive impairment linked to aging, further reinforcing the idea that increased EPA and DHA intake may provide protection to the brain of aged subjects.

Subthalamic stimulation increases striatal tyrosine hydroxylase phosphorylation.

Subthalamic stimulation enhances striatal tyrosine hydroxylase activity, which is regulated by phosphorylation at different serine residues. Western blotting was performed to investigate phosphorylation at the serine residues 19, 31 and 40 in striatal tissue of rats that had received subthalamic stimulation or sham stimulation for 2 h. In animals that were killed directly after stimulation, the tyrosine hydroxylase protein content was unchanged, whereas phosphorylation at the serine residue 19 was increased and phosphorylation at the serine residues 31 and 40 tended to be higher compared with controls. By contrast, tyrosine hydroxylase protein content and phosphorylation were similar in rats that were killed 24 h after stimulation. Our results suggest that subthalamic stimulation may increase tyrosine hydroxylase activity via increased phosphorylation.