Targeting Phospholipase D4 attenuates kidney fibrosis by modulating immune system and activating proteases

Phospholipase D4 (PLD4), a single pass transmembrane glycoprotein, is amongst the most highly upregulated genes in mice kidneys subjected to chronic progressive fibrosis1. Here we characterized the expression pattern of PLD4 and found it to be over expressed in the proximal and distal tubular epithelial cells of mice and human kidneys following fibrosis. Subcellularly, PLD4 was localized to the endoplasmic reticulum, golgi apparatus and mitochondria and was confirmed to interact with Calmegin, Lectin, Mannose Binding 2 and Suppressor of Lin-12-Like Protein 1. Mechanistically, we show that PLD4 facilitates fibrogenesis by modulating innate and adaptive immune system thereby promoting TGF-β signaling pathway. Moreover, PLD4 induces the expression of α1-antitrypsin protein (AAT, a serine protease inhibitor) that results in subsequent down-regulation of Neutrophil Elastase (NE), thereby leading to the accumulation of extracellular proteins and scar tissue formation. Genetic silencing of PLD4 protected mice from development of fibrosis initiated by either Folic acid (FA) treatment or unilateral ureteral obstruction (UUO). Furthermore, therapeutic targeting of PLD4 using specific siRNA also protected the mice from kidney fibrosis via the same mechanisms. These results suggest that inhibition of PLD4 is sufficient to activate protease-mediated degradation of extracellular matrix and reversal of fibrosis thereby highlighting new therapeutic strategies.