Mouse models of human INAD by Pla2g6 deficiency

Infantile neuroaxonal dystrophy (INAD) is a severe neurodegenerative disease characterized by its early onset. PLA2G6, which encodes a phospholipase A2, iPLA₂β, has been identified as a causative gene of INAD. iPLA₂β has been shown to be involved in various physiological and pathological processes, including immunity, cell death, and cell membrane homeostasis. Gene targeted mice with a null mutation of Pla2g6 develop the INAD phenotype as late as approximately 1 to 2 years after birth. Recently, another INAD mouse model, Pla2g6-INAD mice line, has been established. The Pla2g6-INAD mice bear a point mutation in the ankyrin repeat domain of Pla2g6 generated by N-ethyl-N-nitrosourea mutagenesis. These mutant mice develop severe motor dysfunction and hematopoietic abnormality in a manner following Mendelian law. The mice showed the abnormal gait and poor performance as early as 7 to 8 weeks of age, detected by hanging grip test. Neuropathological examination revealed widespread formation of spheroids containing tubulovesicular membranes similar to human INAD. Molecular and biochemical analysis revealed that the mutant mice expressed Pla2g6 mRNA and protein, but the mutated Pla2g6 protein had no glycerophospholipid-catalyzing enzyme activity. When analyzed the offspring which bear Pla2g6 knockout allele and Pla2g6-INAD allele, abnormal gait appeared slightly later than Pla2g6-INAD homozygotes but with earlier onset than the Pla2g6 knockout homozygotes. This result suggests that mutant Pla2g6 protein contributes to early onset of INAD symptoms in the absence of intact Pla2g6 protein. The analysis of various INAD mouse models may help to understand the pathogenesis of neurodegenerative diseases, including INAD.