Awakening neural survival mechanisms after stroke: Lipid metabolism in brain-autonomous repair.

In this issue of Neuron, Nakamura et al.1 report the discovery that neuronally secreted phospholipase PLA2G2E releases dihomo-γ-linolenic acid (DGLA) that generates 15-hydroxy-eicosatrienoic acid (15-HETrE), which in turn induces peptidyl arginine deiminase 4 (PAD4/PADI4) to elicit neuronal pro-survival and pro-reparative events following ischemic brain injury.

NPD1 Plus RvD1 Mediated Ischemic Stroke Penumbra Protection Increases Expression of Pro-homeostatic Microglial and Astrocyte Genes.

Neuroprotection to attenuate or block the ischemic cascade and salvage neuronal damage has been extensively explored for treating ischemic stroke. However, despite increasing knowledge of the physiologic, mechanistic, and imaging characterizations of the ischemic penumbra, no effective neuroprotective therapy has been found. This study focuses on the neuroprotective bioactivity of docosanoid mediators: Neuroprotectin D1 (NPD1), Resolvin D1 (RvD1), and their combination in experimental stroke. Molecular targets of NPD1 and RvD1 are defined by following dose-response and therapeutic window. We demonstrated that treatment with NPD1, RvD1, and combination therapy provides high-grade neurobehavioral recovery and decreases ischemic core and penumbra volumes even when administered up to 6 h after stroke. The expression of the following genes was salient: (a) Cd163, an anti-inflammatory stroke-associated gene, was the most differentially expressed gene by NPD1+RvD1, displaying more than a 123-fold upregulation in the ipsilesional penumbra (Lisi et al., Neurosci Lett 645:106-112, 2017); (b) 100-fold upregulation takes place in astrocyte gene PTX3, a key regulator of neurogenesis and angiogenesis after cerebral ischemia (. Rodriguez-Grande et al., J Neuroinflammation 12:15, 2015); and (c) Tmem119 and P2y12, two markers of homeostatic microglia, were found to be enhanced by ten- and fivefold, respectively (Walker et al. Int J Mol Sci 21:678, 2020). Overall, we uncovered that protection after middle cerebral artery occlusion (MCAo) by the lipid mediators elicits expression of microglia and astrocyte-specific genes (Tmem119, Fcrls, Osmr, Msr1, Cd68, Cd163, Amigo2, Thbs1, and Tm4sf1) likely participating in enhancing homeostatic microglia, modulating neuroinflammation, promoting DAMP clearance, activating NPC differentiation and maturation, synapse integrity and contributing to cell survival.

Retina and RPE lipid profile changes linked with ABCA4 associated Stargardt's maculopathy.

Stargardt maculopathy, caused predominantly by mutations in the ABCA4 gene, is characterized by an accumulation of non-degradable visual pigment derivative, lipofuscin, in the retinal pigment epithelium (RPE) - resulting in RPE atrophy. RPE is a monolayer tissue located adjacent to retinal photoreceptors and regulates their health and functioning; RPE atrophy triggers photoreceptor cell death and vision loss in Stargardt patients. Previously, ABCA4 mutations in photoreceptors were thought to be the major contributor to lipid homeostasis defects in the eye. Recently, we demonstrated that ABCA4 loss of function in the RPE leads to cell-autonomous lipid homeostasis defects. Our work underscores that an incomplete understanding of lipid metabolism and lipid-mediated signaling in the retina and RPE are potential causes for lacking treatments for this disease. Here we report altered lipidomic in mouse and human Stargardt models. This work provides the basis for therapeutics that aim to restore lipid homeostasis in the retina and the RPE.