Distribution of Alox15 in the Rat Brain and Its Role in Prefrontal Cortical Resolvin D1 Formation and Spatial Working Memory

Abstract

Docosahexaenoic acid (DHA) is enriched in membrane phospholipids of the central nervous system (CNS) and has a role in aging and neuropsychiatric disorders. DHA is metabolized by the enzyme Alox15 to 17S-hydroxy-DHA, which is then converted to 7S-hydroperoxy,17S-hydroxy-DHA by a 5-lipoxygenase, and thence via epoxy intermediates to the anti-inflammatory molecule, resolvin D1 (RvD1 or 7S,8R,17S-trihydroxy-docosa-Z,9E,11E,13Z,15E,19Z-hexaenoic acid). In this study, we investigated the distribution and function of Alox15 in the CNS. RT-PCR of the CNS showed that the prefrontal cortex exhibits the highest Alox15 mRNA expression level, followed by the parietal association cortex and secondary auditory cortex, olfactory bulb, motor and somatosensory cortices, and the hippocampus. Western blot analysis was consistent with RT-PCR data, in that the prefrontal cortex, cerebral cortex, hippocampus, and olfactory bulb had high Alox15 protein expression. Immunohistochemistry showed moderate staining in the olfactory bulb, cerebral cortex, septum, striatum, cerebellar cortex, cochlear nuclei, spinal trigeminal nucleus, and dorsal horn of the spinal cord. Immuno-electron microscopy showed localization of Alox15 in dendrites, in the prefrontal cortex. Liquid chromatography mass spectrometry analysis showed significant decrease in resolvin D1 levels in the prefrontal cortex after inhibition or antisense knockdown of Alox15. Alox15 inhibition or antisense knockdown in the prefrontal cortex also blocked long-term potentiation of the hippocampo-prefrontal cortex pathway and increased errors in alternation, in the T-maze test. They indicate that Alox15 processing of DHA contributes to production of resolvin D1 and LTP at hippocampo-prefrontal cortical synapses and associated spatial working memory performance. Together, results provide evidence for a key role of anti-inflammatory molecules generated by Alox15 and DHA, such as resolvin D1, in memory. They suggest that neuroinflammatory brain disorders and chronic neurodegeneration may ‘drain’ anti-inflammatory molecules that are necessary for normal neuronal signaling, and compromise cognition.

Expression of DHA-Metabolizing Enzyme Alox15 is Regulated by Selective Histone Acetylation in Neuroblastoma Cells

“…In contrast, the mature brain is less sensitive to such effects [ 56 ]. In view of our recent findings of a role of Alox15 in synaptic plasticity [ 15 ] and this study, we postulate that one such environmental influence that can affect learning and memory in the developing brain, may take the form of epigenetic effects on Alox15 and metabolites of DHA. Further work is necessary to elucidate the detailed mechanisms of effect of histone acetylation on Alox15 expression.…”

“…Recently, Alox15 has been found to have effects on synaptic plasticity. Antisense knockdown of the enzyme in the rat prefrontal cortex results in reduced levels of resolvin D1 and deficits in hippocampo-prefrontal cortical long-term-potentiation (LTP) and spatial working memory [ 15 ]. Alox15 inhibition in the prefrontal cortex reduces the anti-nociceptive effect of a DHA-rich nutraceutical, in a mouse model of neuropathic orofacial pain, suggesting a role of the enzyme in supraspinal antinociception [ 16 ].…”

Localisation of Formyl-Peptide Receptor 2 in the Rat Central Nervous System and Its Role in Axonal and Dendritic Outgrowth

“…There is much recent interest in the role of lipid mediators as signalling molecules in the brain. In particular, recent findings suggest that lipid anti-inflammatory molecules could have a role in processes such as long term potentiation and memory formation [ 33 – 37 ]. However, the contribution of FPR2 to axonal or dendritic outgrowth is unknown.…”

n-3 Polyunsaturated Fatty Acids and Their Derivates Reduce Neuroinflammation during Aging

“…Of note, higher levels of brain RvD1 in Fat-1 mice, owing to higher brain n-3 LC-PUFAs induced by genetic means, are linked to less cognitive deficits, a reduction in microglial activation, and in pro-inflammatory status following brain ischemia [168,169]. Conversely, lower levels of brain RvD1, owing to 15-LOX inhibition, are related to alterations in working memory and synaptic plasticity in rats [97].…”

“…15-LOX mRNA expression increases in n-3 LC-PUFA supplemented group and decreases in n-3 LC-PUFA deficient diet [100,244,245]. 15-LOX generates both 15-HETEs that inhibit NFκB [103] as well as RvD1 that contributes to the preservation of cognitive performance [97].…”