Cyclooxygenase-2 and n-6 PUFA are lower and DHA is higher in the cortex of fat-1 mice
Introduction
Docosahexaenoic acid (DHA) and arachidonic acid (AA) are polyunsaturated fatty acids (PUFA) which are highly enriched in brain plasma membrane phospholipids (Diau et al., 2005). DHA and AA are 22 and 20 carbon PUFA, respectively. DHA belongs to the n-3 while AA belongs to the n-6 family of fatty acids. The n-3 and n-6 nomenclature refers to the position of the first double bond relative to the methyl terminus. Relative to the diet, DHA is primarily obtained from marine oils while AA is found in animal fat.
It has been reported that DHA may be protective against neurological diseases and cognitive decline (Lim et al., 2005a, van Gelder et al., 2007). In contrast, AA is associated with inflammatory events in the brain which may increase risk for neurodegenerative diseases (Farooqui et al., 2007). After being cleaved and released from the plasma membrane by phospholipase A2 (PLA2), AA can be metabolized into pro-inflammatory prostaglandins by cyclooxygenase-2 (COX-2) (Farooqui et al., 2007). Deprivation of dietary n-3 PUFA in rats for 15 weeks, resulting in lower brain n-3 PUFA and higher n-6 PUFA, has been shown to increase the expression of enzymes associated with the AA inflammatory pathway such as cytosolic phospholipase A2 (cPLA2) and COX-2 (Rao et al., 2007).
It is important to note that n-3 PUFA and n-6 PUFA cannot be interconverted or formed de novo by mammals due to the lack of appropriate desaturase enzymes. Linoleic and α-linolenic acid obtained from the diet can be elongated and desaturated to form long chain PUFA including, AA and DHA but the rate of conversion is very low (Pawlosky et al., 2001, James et al., 1993).
The fat-1 transgenic mouse is able to convert n-6 to n-3 PUFA due to the expression of the fat-1 gene from Caenorhabditis elegans which encodes for an n-3 desaturase (Kang et al., 2004). n-3 PUFA enrichment and n-6 PUFA reduction have been reported in total lipid extracts from whole brains of the fat-1 mouse which appear to mimic effects observed after n-3 feeding (Kang et al., 2004, Taha et al., 2008, Lim et al., 2005b). These observations suggest a potential utility of the fat-1 mouse model to study the role of DHA and AA in brain physiology and disease. Given that these major n-3 and n-6 fatty acids play a role in initiating anti-inflammatory and pro-inflammatory signalling pathways, detailed phenotypic characterization of the origins of these biologically active fatty acids is needed, which reside in membrane phospholipids is lacking. Furthermore, no fatty acid data has been reported in the literature for specific brain regions in the fat-1 mouse. These data are fundamental to validating the utility of the fat-1 genetic model to study the relationship between AA, DHA and inflammatory processes. Therefore, the objectives of this study are to determine the phospholipid fatty acid composition in the brain cortex and effects of the fat-1 gene on cPLA2 and COX-2 expression in the cortex.
Section snippets
Animals and diet
Heterozygous fat-1 males on a mixed C57BL/6 × C3H background were bred with wildtype (WT) C57BL/6 females (Charles River, Saint-Constant, Quebec, Canada) to produce heterozygous fat-1+/− and WT mice. All mice were fed a modified n-6 PUFA enriched and n-3 PUFA deficient AIN-93G diet containing 10% of safflower oil instead of 7% soybean oil (Product #D04092701; Research Diets, New Brunswick, NJ). This model permits the characterization of effects of n-3 deficiency in WT mice while fat-1 mice are
Fatty acid composition of phospholipids and sphingomyelin in the cortex of the fat-1 mouse
As shown in Fig. 1, DHA was approximately 3 times higher in phospholipid and sphingomyelin fractions of the fat-1 mouse cortex when compared to WT (p < 0.05). Because the fat-1 mouse converts n-6 PUFA to n-3 PUFA, this also results in 26%, 49% and 77% lower (p < 0.05) levels of n-6 PUFA in glycerophosphocholine, glycerophosphoethanolamine and glycerophosphoserine, respectively, in fat-1 mice. The lower DHA in WT mice was compensated by the presence of the 22 carbon, 5 double bond, n-6 PUFA,
Discussion
In this study, detailed fatty acid analysis of the cortex showed higher levels of DHA in fat-1 mice compared to n-3 PUFA deficient WT controls. Although total lipid analyses would have been simpler, it does not provide the level of detail in order to ascertain whether changes in fatty acid composition due the fat-1 gene are comparable to existing literature values. Fatty acids results demonstrate that n-3 PUFA, specifically DHA, are higher in all phospholipids fractions of the fat-1 mouse
Acknowledgments
Funding from the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grants were provided to D.W.L. Ma and R.P. Bazinet. Funding from the J.P. Bickel Foundation for Medical Research and Connaught Fund were also provided to D.W.L. Ma. C. Boudrault is supported by a Canada Graduate Scholarship through NSERC.
References (40)
- et al.
The low density lipoprotein receptor is not necessary for maintaining mouse brain polyunsaturated fatty acid concentrations
J. Lipid Res.
(2008) - et al.
Age-related changes in phospholipid fatty acid composition and monoaminergic neurotransmission in the hippocampus of rats fed a balanced or an n-3 polyunsaturated fatty acid-deficient diet
J. Lipid Res.
(1997) - et al.
n-3 PUFAs modulate T-cell activation via protein kinase C-alpha and -epsilon and the NF-kappaB signaling pathway
J. Lipid Res.
(2005) - et al.
A simple method for the isolation and purification of total lipides from animal tissues
J. Biol. Chem.
(1957) - et al.
Simple relationships exist between dietary linoleate and the n-6 fatty acids of human neutrophils and plasma
Am. J. Clin. Nutr.
(1993) - et al.
Cyclooxygenases and the central nervous system
Prostaglandins
(1997) - et al.
Novel docosanoids inhibit brain ischemia-reperfusion-mediated leukocyte infiltration and pro-inflammatory gene expression
J. Biol. Chem.
(2003) Distinct functions of COX-1 and COX-2
Prostaglandins Other Lipid Mediat.
(2002)- et al.
Cyclooxygenase-2 expression is increased in frontal cortex of Alzheimer's disease brain
Neuroscience
(1998) - et al.
Physiological compartmental analysis of alpha-linolenic acid metabolism in adult humans
J. Lipid Res.
(2001)
Cyclooxygenases, lipoxygenases, and epoxygenases in CNS: their role and involvement in neurological disorders
Brain Res. Rev.
Postmortem studies in mood disorders indicate altered numbers of neurons and glial cells
Biol. Psychiatry
The molecular pathology of Alzheimer's disease
Neuron
Cytosolic phospholipase A2 (cPLA2) immunoreactivity is elevated in Alzheimer's disease brain
Neurobiol. Dis.
Fish consumption, n-3 fatty acids, and subsequent 5-y cognitive decline in elderly men: the Zutphen Elderly Study
Am. J. Clin. Nutr.
n-3 polyunsaturated fatty acid (PUFA) deficiency elevates and n-3 PUFA enrichment reduces brain 2-arachidonoylglycerol level in mice
Prostaglandins Leukot. Essent. Fatty Acids
Expression of a mitogen-inducible cyclooxygenase in brain neurons: regulation by synaptic activity and glucocorticoids
Neuron
Transcriptional roles of nuclear factor kappa B and nuclear factor-interleukin-6 in the tumor necrosis factor alpha-dependent induction of cyclooxygenase-2 in MC3T3-E1 cells
J. Biol. Chem.
Distribution of cyclooxygenase-1 and cyclooxygenase-2 mRNAs and proteins in human brain and peripheral organs
Brain Res.
Receptor-mediated activation of phospholipase A2 and arachidonic acid release in signal transduction
Biochem. Soc. Trans.
Cited by (22)
n-3 long-chain PUFA-containing phospholipids and neuroprotection
2019, Omega Fatty Acids in Brain and Neurological HealthInterplay between lipid mediators and immune system in the promotion of brain self-repair
2017, Role of the Mediterranean Diet in the Brain and Neurodegenerative DiseasesModulation of brain PUFA content in different experimental models of mice
2016, Prostaglandins Leukotrienes and Essential Fatty AcidsCitation Excerpt :The fatty acid composition varied within the different brain regions confirming several previous reports [5,8,31]. In response to dietary n-3 PUFA deficiency or to a genetic-driven enrichment in n-3 PUFAs, all brain regions were impacted in terms of AA and DHA variations as already reported [5,6,12,32–37]. Yet, some structures were more affected than others.
Endogenous synthesis of n-3 PUFA modifies fatty acid composition of kidney phospholipids and eicosanoid levels in the fat-1 mouse
2013, Prostaglandins Leukotrienes and Essential Fatty AcidsCould heterotopic ossification be prevented by varying dietary n-3/n-6 polyunsaturated fatty acid ratio: A novel perspective to its treatment?
2013, Medical HypothesesCitation Excerpt :Combined with the previously described notion that PGE2, derived from arachidonic acid, is believed to mediate the inflammation in the HO formation as the key factor, Lowering the dietary (n-6)/(n-3) PUFAs ratio may reduce arachidonic acid synthesis, subsequently impair its conversion to PGE2 by COX-2, which may prevent HO. In addition, recent investigations from in vitro culture system and transgenic animal models proposed that modifying the dietary (n-6)/(n-3) PUFA ratio to a lower level may block COX-2 expression and its activity [33–36]. A clinical trial has been reported by Caughey et al. that enriching diet with n-3 PUFAs by fish oil supplement, increases the cyclooxygenase inhibitory activity of paracetamol in rheumatoid arthritis patients [37], whilst Horia et al. suggested that n-3 PUFAs could exert a complementary inhibitory on COX-2 activity in breast cancer cell line [38].