Identification of Leptospira interrogans Phospholipase C as a Novel Virulence Factor Responsible for Intracellular Free Calcium Ion Elevation during Macrophage Death

Jing Fang Zhao, Hong Hu Chen, David M. Ojcius, Xin Zhao, Dexter Sun, Yu Mei Ge, Lin Li Zheng, Xu'ai Lin, Lan Juan Li*, Jie Yan

*Corresponding author for this work

Research output: Contribution to journalJournal Article peer-review

25 Scopus citations

Abstract

Background:Leptospira-induced macrophage death has been confirmed to play a crucial role in pathogenesis of leptospirosis, a worldwide zoonotic infectious disease. Intracellular free Ca2+ concentration ([Ca2+]i) elevation induced by infection can cause cell death, but [Ca2+]i changes and high [Ca2+]i-induced death of macrophages due to infection of Leptospira have not been previously reported.Methodology/Principal Findings:We first used a Ca2+-specific fluorescence probe to confirm that the infection of L. interrogans strain Lai triggered a significant increase of [Ca2+]i in mouse J774A.1 or human THP-1 macrophages. Laser confocal microscopic examination showed that the [Ca2+]i elevation was caused by both extracellular Ca2+ influx through the purinergic receptor, P2X7, and Ca2+ release from the endoplasmic reticulum, as seen by suppression of [Ca2+]i elevation when receptor-gated calcium channels were blocked or P2X7 was depleted. The LB361 gene product of the spirochete exhibited phosphatidylinositol phospholipase C (L-PI-PLC) activity to hydrolyze phosphatidylinositol-4,5-bisphosphate (PIP2) into inositol-1,4,5-trisphosphate (IP3), which in turn induces intracellular Ca2+ release from endoplasmic reticulum, with the Km of 199 μM and Kcat of 8.566E-5 S-1. Secretion of L-PI-PLC from the spirochete into supernatants of leptospire-macrophage co-cultures and cytosol of infected macrophages was also observed by Western Blot assay. Lower [Ca2+]i elevation was induced by infection with a LB361-deficient leptospiral mutant, whereas transfection of the LB361 gene caused a mild increase in [Ca2+]i. Moreover, PI-PLCs (PI-PLC-β3 and PI-PLC-γ1) of the two macrophages were activated by phosphorylation during infection. Flow cytometric detection demonstrated that high [Ca2+]i increases induced apoptosis and necrosis of macrophages, while mild [Ca2+]i elevation only caused apoptosis.Conclusions/Significance:This study demonstrated that L. interrogans infection induced [Ca2+]i elevation through extracellular Ca2+ influx and intracellular Ca2+ release cause macrophage apoptosis and necrosis, and the LB361 gene product was shown to be a novel PI-PLC of L. interrogans responsible for the [Ca2+]i elevation.

Original languageEnglish
Article numbere75652
JournalPLoS ONE
Volume8
Issue number10
DOIs
StatePublished - 04 10 2013
Externally publishedYes

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