PLD4 Is Involved in Phagocytosis of Microglia: Expression and Localization Changes of PLD4 Are Correlated with Activation State of Microglia

Abstract

Phospholipase D4 (PLD4) is a recently identified protein that is mainly expressed in the ionized calcium binding adapter molecule 1 (Iba1)-positive microglia in the early postnatal mouse cerebellar white matter. Unlike PLD1 and PLD2, PLD4 exhibits no enzymatic activity for conversion of phosphatidylcholine into choline and phosphatidic acid, and its function is completely unknown. In the present study, we examined the distribution of PLD4 in mouse cerebellar white matter during development and under pathological conditions. Immunohistochemical analysis revealed that PLD4 expression was associated with microglial activation under such two different circumstances. A primary cultured microglia and microglial cell line (MG6) showed that PLD4 was mainly present in the nucleus, except the nucleolus, and expression of PLD4 was upregulated by lipopolysaccharide (LPS) stimulation. In the analysis of phagocytosis of LPS-stimulated microglia, PLD4 was co-localized with phagosomes that contained BioParticles. Inhibition of PLD4 expression using PLD4 specific small interfering RNA (siRNA) in MG6 cells significantly reduced the ratio of phagocytotic cell numbers. These results suggest that the increased PLD4 in the activation process is involved in phagocytosis of activated microglia in the developmental stages and pathological conditions of white matter.

PLD4 promotes M1 macrophages to perform antitumor effects in colon cancer cells

“…furthermore, phospholipase D4 is a member of the family of phospholipid enzymes (14), and is mainly expressed in spleen and early microglia (15). Recent studies showed two autoimmune diseases, sclerosis and rheumatoid arthritis, were related to PLD4 mutation (16,17).…”

“…But unlike PLD1 and PLD2, PLD4 exhibited no enzymatic activity for transforming phosphatidylcholine into choline and phosphatidic acid (14). After treated with LPS, the expression of the PLD4 in microglia was increased which could promote the function of phagocytosis (15). Recent studies have indicated mutation in PLD4 gene was associated with two autoimmune diseases, named systemic sclerosis (16) and rheumatoid arthritis (17), both had abnormal inflammatory skin lesions symptoms (18).…”

Thematic Review Series: Phospholipases: Central Role in Lipid Signaling and Disease

“…Initial reports described PLD4 expression in microglia, the macrophage-like innate immune cells of the CNS, as well as in splenic cells, presumably macrophages. PLD4 expression increases with microglial activation, which is also characterized by increased phagocytic capacity ( 34,98 ). siRNA knockdown of PLD4 suppressed phagocytosis, suggesting a role for PLD4 in the setting of CNS injury and infection ( 34,98 ).…”

“…PLD4 expression increases with microglial activation, which is also characterized by increased phagocytic capacity ( 34,98 ). siRNA knockdown of PLD4 suppressed phagocytosis, suggesting a role for PLD4 in the setting of CNS injury and infection ( 34,98 ). A nonsense mutation in PLD4 (W215X) in Fleckvieh cattle causes severe skin lesions, generally poor health, and decreased survival ( 99 ).…”

Morphological, immunocytochemical and functional characterization of the microglial phenotype in culture

“…Earlier attempts to characterize microglial cells in vitro frequently employed culturing times of less than a week Tanaka et al, 1998;Otani et al, 2011), when changes in microglial population dynamics were not always apparent. Microglia cultured from the embryonic or from the adult brain were also found to differ in many important ways.…”