Characterizing the Role of Phospholipase A₂ Enzymes in Inflammatory Signaling

Abstract

Cell membranes are not merely structural barriers, their precise lipid composition actively shapes cellular signaling and inflammatory responses. Phospholipid remodeling enzymes are central to this regulation, with calcium-independent phospholipase A2 (iPLA2/PLA2G6) controlling membrane homeostasis by hydrolyzing membrane phospholipids into lysophospholipids and free fatty acids. While iPLA2 has been extensively studied in neurons, where its loss-of-function underlies PLA2G6-associated neurodegeneration (PLAN), its role in innate immune cells has remained largely unexplored. Given that macrophage inflammatory responses critically depend on membrane lipid organization and lipid-derived mediators, the functional relevance of iPLA2 in these cells represents a significant gap in our understanding. Here I show that iPLA2 expression is a necessary prerequisite for efficient induction of pro-inflammatory responses in human macrophages. Using siRNA-mediated knockdown in primary monocyte-derived macrophages, I demonstrated that iPLA2 knockdown broadly attenuated Toll-like receptor (TLR) responsiveness, substantially reducing cytokine and chemokine release across multiple inflammatory stimuli. This attenuated TLR response extended to inflammasome activation: iPLA2 knockdown reduced expression of NLRP3 and pro-IL-1β, impairing inflammasome priming and culminating in significantly reduced IL-1β secretion. Mechanistically, iPLA2 knockdown did not alter NF-κB (p65) or p38 MAPK phosphorylation, suggesting that iPLA2 acts through an alternative pathway. Strikingly, iPLA2 depletion profoundly reshaped the cellular lipid landscape, driving accumulation of neutral lipid species and lipid droplets. This consequence of iPLA2 depletion has not been described before and likely underlies the inflammatory deficit. These findings establish iPLA2 expression as a key determinant of the human macrophage inflammatory program, linking phospholipid turnover to the capacity for effective immune activation. Given the emerging connection between neuroinflammation and neurodegenerative diseases in which iPLA2 is already implicated, my results raise the possibility that iPLA2 dysfunction in human macrophages and microglia may contribute to disease pathology beyond the neuronal compartment, opening new avenues for therapeutic intervention.