Mitochondrial structural and functional defects in the Drosophila melanogaster model of PLA2G6 Associated Neurodegeneration (PLAN)

Abstract

PLA2G6-associated neurodegeneration (PLAN) is a rare progressive disorder caused by mutations in PLA2G6, which encodes calcium-independent phospholipase A2, an enzyme required for phospholipid remodeling and membrane lipid homeostasis through the Lands cycle. Although mitochondrial dysfunction has been implicated in PLAN, how PLA2G6 loss affects mitochondrial structure and function across tissues, age, and sex remains unclear. Here, we used homozygous null iPLA2-VIA mutant Drosophila melanogaster, a model of PLAN, to examine mitochondrial ultrastructure, abundance, function, DNA content, and mitochondrial maintenance gene expression. Transmission electron microscopy revealed severe mitochondrial abnormalities in the brain, thorax, and ovary from 7-day-old and 3-week-old mutant flies, including disrupted cristae, abnormal morphology, and compromised membrane structure. Mutants also showed reduced mitochondrial number, which became more widespread with age. MitoTracker imaging further showed reduced mitochondrial staining and abnormal clumped mitochondrial distribution in mutant brains. Consistent with mitochondrial depletion, mitochondrial DNA content was reduced in mutants, with decreased ATPase6 but unchanged nuclear ATPSynC levels. Functionally, mutants exhibited reduced ATP production across multiple tissues and at the whole-body level, while ROS levels changed in a tissue-, age-, and sex-dependent manner. Transcript analysis showed reduced mTOR and PGC-1 expression, altered expression of fusion and fission genes including Opa1, Drp1, and Fis1, age- and sex-dependent changes in Pink1, reduced Trap1 expression in aged mutants, and unchanged Sirtuin 6 expression. Together, these findings show that iPLA2-VIA is required for mitochondrial maintenance and bioenergetic integrity in vivo.