Impaired iPLA2β activity affects iron uptake and storage without iron accumulation: An in vitro study excluding decreased iPLA2β activity as the cause of iron deposition in PLAN

PLA2G6-associated neurodegeneration (PLAN, NBIA2) is the second most common type of neurodegeneration with brain iron accumulation (NBIA), caused by recessive mutations of PLA2G6 gene, which encodes Ca2+-independent phospholipase A2β (iPLA2β). In most PLAN cases, decreased iPLA2β activity and iron deposition was observed meanwhile, and researchers also identified a PLA2G6 mutation family without iron deposition shown by MRI images. This brought us the question of whether decreased iPLA2β activity was the cause of iron deposition in PLAN. In this study, we used S-BEL as the antagonist of iPLA2β to block its activity and used SH-SY5Y cells as the expression system. We incubated SH-SY5Y cells with different concentrations of S-BEL. The results showed that decreased iPLA2β activity led no obvious iron accumulation, while changes of cells state and activation of apoptosis were observed. To further investigate the cause of unchanged iron level, we examined the cellular iron regulatory proteins involved in iron uptake, storage and export. The results were as follows: TfR1 (iron uptake protein) expression was decreased, the expression of ferritin heavy chain and light chain (iron storage protein) was increased. There was no alteration of the expression of DMT1 (iron uptake protein) and FPN1 (iron export protein). Under the condition of decreased iPLA2β activity, there was no obvious iron accumulation but iron uptake activity decreased and iron storage activity increased. Therefore, we speculate that the decreased iPLA2β activity may not be the main reason for iron deposition in PLAN.