title: Neuroaxonal dystrophy in PLA2G6 knockout mice.
abstract: The PLA2G6 gene encodes group VIA calcium-independent phospholipase A2 (iPLA2 β), which belongs to the PLA2 superfamily that hydrolyses the sn-2 ester bond in phospholipids. In the nervous system, iPLA2 β is essential for remodeling membrane phospholipids in axons and synapses. Mutated PLA2G6 causes PLA2G6-associated neurodegeneration (PLAN) including infantile neuroaxonal dystrophy (INAD) and adult-onset dystonia-parkinsonism (PARK14), which have unique clinical phenotypes. In the PLA2G6 knockout (KO) mouse, which is an excellent PLAN model, specific membrane degeneration takes place in neurons and their axons, and this is followed by axonal spheroid formation. These pathological findings are similar to those in PLAN. This review details the evidence that membrane degeneration of mitochondria and axon terminals is a precursor to spheroid formation in this disease model. From a young age before the onset, many mitochondria with damaged inner membranes appear in PLA2G6 KO mouse neurons. These injured mitochondria move anterogradely within the axons, increasing in the distal axons. As membrane degeneration progresses, the collapse of the double membrane of mitochondria accompanies axonal injury near impaired mitochondria. At the axon terminals, the membranes of the presynapses expand irregularly from a young age. Over time, the presynaptic membrane ruptures, causing axon terminal degeneration. Although these processes occur in different degenerating membranes, both contain tubulovesicular structures, which are a specific ultrastructural marker of INAD. This indicates that two unique types of membrane degeneration underlie PLAN pathology. We have shown a new pathological mechanism whereby axons degenerate due to defective maintenance and rupture of both the inner mitochondrial and presynaptic membranes. This degeneration mechanism could possibly clarify the pathologies of PLAN, Parkinson disease and neurodegeneration with iron accumulation (NBIA), which are assumed to be due to the primary degeneration of axons.
authors.affiliation: Department of Neurology, Osaka University Graduate School of Medicine, Suita, Japan.
authors.forename: Hisae
authors.initials: H
authors.lastname: Sumi-Akamaru
authors.affiliation: Department of Neurology, Osaka University Graduate School of Medicine, Suita, Japan.
authors.forename: Goichi
authors.initials: G
authors.lastname: Beck
authors.affiliation: Division of Neuropathology, Department of Brain and Neurosciences, Tottori University Faculty of Medicine, Yonago, Japan.
authors.forename: Shinsuke
authors.initials: S
authors.lastname: Kato
authors.affiliation: Department of Neurology, Osaka University Graduate School of Medicine, Suita, Japan.
authors.forename: Hideki
authors.initials: H
authors.lastname: Mochizuki
mesh_terms: D000818:Animals; D001369:Axons / Q000473:pathology; D001921:Brain / Q000473:pathology; D004195:Disease Models, Animal; D018450:Disease Progression; D020404:Glycerophospholipids / Q000378:metabolism; D054522:Group VI Phospholipases A2 / Q000235:genetics*; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D008928:Mitochondria / Q000648:ultrastructure; D019150:Neuroaxonal Dystrophies / Q000235:genetics* / Q000378:metabolism / Q000473:pathology*; D009474:Neurons / Q000648:ultrastructure; D018384:Oxidative Stress; D010525:Peripheral Nerves / Q000473:pathology; D013116:Spinal Cord / Q000473:pathology
chemical_list: D020404:Glycerophospholipids; D054522:Group VI Phospholipases A2; C516476:Pla2g6 protein, mouse
keywords: PLA2G6; calcium independent phospholipaseA2β (iPLA2β); infantile neuroaxonal dystrophy (INAD); membrane; mitochondria