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

PLA2G6-associated neurodegeneration (PLAN) is a rare, progressive neurological disorder caused by mutations in the PLA2G6 gene, which encodes the calcium-independent phospholipase A2 enzyme essential for phospholipid remodeling and membrane lipid homeostasis through the Lands cycle. Although mitochondrial dysfunction has been implicated in PLAN, the mechanisms linking PLA2G6 loss to mitochondrial degeneration across tissues, age, and sex remain poorly defined. Drosophila melanogaster (fruit flies) contains the human ortholog of the PLA2G6 gene, called iPLA2-VIA, homozygous mutation of which shows neurodegenerative phenotypes, including severely reduced lifespan, loss of locomotory ability, reduced fecundity, and mitochondrial structural and functional impairment at an early age. Thus, we use the Drosophila melanogaster iPLA2-VIA homozygous mutant flies to systematically examine mitochondrial structure, abundance, function, and the altered gene expression of the genes associated with the mitochondrial biogenesis cycle. Transmission electron microscopy revealed mitochondrial ultrastructural abnormalities in the brain, thorax, and ovary of iPLA2-VIA mutant flies, including disrupted cristae, abnormal mitochondrial morphology, and abnormal membrane integrity. Quantitative analysis demonstrated a significant, age-dependent reduction in mitochondrial number across multiple tissues in both sexes. Consistent with these structural defects, mutant flies exhibited reduced ATP production and altered reactive oxygen species (ROS) levels in a tissue-, age-, and sex-specific manner, indicating impaired mitochondrial bioenergetic capacity. At the transcriptional level, loss of function of iPLA2-VIA significantly altered the expression of genes governing mitochondrial biogenesis and dynamics. Key biogenesis regulators, including mTOR and PGC-1, were downregulated in young mutants, while genes involved in mitochondrial fusion and fission (Opa1, Mfn2, Drp1, and Fis1) showed selective, age- and sex-dependent dysregulation. Collectively, our findings demonstrate that iPLA2-VIA is essential for maintaining mitochondrial integrity, abundance, and bioenergetic function. This work establishes a mechanistic framework linking disrupted phospholipid remodeling to mitochondrial degeneration in PLAN. It highlights Drosophila as a powerful model for dissecting age- and sex-dependent mitochondrial pathology in neurodegenerative disease.