PKC/ROS-Mediated NLRP3 Inflammasome Activation Is Attenuated by Leishmania Zinc-Metalloprotease during Infection

Our plain-English summary of PKC/ROS-Mediated NLRP3 Inflammasome Activation Is Attenuated by Leishmania Zinc-Metalloprotease during Infection, by M.T. Shio, J.G. Christian, J.Y. Jung, et al (PLoS Neglected Tropical Diseases, 2015).

The study

• Authors: M.T. Shio, J.G. Christian, J.Y. Jung, K.P. Chang, M. Olivier
• Journal: PLoS Neglected Tropical Diseases
• Published: 2015;9(6):e0003868
• Cited by: 82 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Parasites of the Leishmania genus infect and survive within macrophages by inhibiting several microbicidal molecules, such as nitric oxide and pro-inflammatory cytokines. In this context, various species of Leishmania have been reported to inhibit or reduce the production of IL-1β both in vitro and in vivo. However, the mechanism whereby Leishmania parasites are able to affect IL-1β production and secretion by macrophages is still not fully understood. Dependent on the stimulus at hand, the maturation of IL-1β is facilitated by different inflammasome complexes. The NLRP3 inflammasome has been shown to be of pivotal importance in the detection of danger molecules such as inorganic crystals like asbestos, silica and malarial hemozoin, (HZ) as well as infectious agents. In the present work, we investigated whether Leishmania parasites modulate NLRP3 inflammasome activation. Using PMA-differentiated THP-1 cells, we demonstrate that Leishmania infection effectively inhibits macrophage IL-1β production upon stimulation. In this context, the expression and activity of the metalloprotease GP63 - a critical virulence factor expressed by all infectious Leishmania species - is a prerequisite for a Leishmania-mediated reduction of IL-1β secretion. Accordingly, L. mexicana, purified GP63 and GP63-containing exosomes, caused the inhibition of macrophage IL-1β production. Leishmania-dependent suppression of IL-1β secretion is accompanied by an inhibition of reactive oxygen species (ROS) production that has previously been shown to be associated with NLRP3 inflammasome activation. The observed loss of ROS production was due to an impaired PKC-mediated protein phosphorylation. Furthermore, ROS-independent inflammasome activation was inhibited, possibly due to an observed GP63-dependent cleavage of inflammasome and inflammasome-related proteins. Collectively for the first time, we herein provide evidence that the protozoan parasite Leishmania, through its surface metalloprotease GP63, can significantly inhibit NLRP3 inflammasome function and IL-1β production.

In plain English

This was a laboratory study of cells, not of people exposed to asbestos. The authors examined whether Leishmania, the parasite that causes leishmaniasis, interferes with the NLRP3 inflammasome. This is a multi-protein complex inside cells that converts an inactive precursor into the inflammatory signal IL-1β in response to crystals such as malarial hemozoin, silica and asbestos. They used a human cell line (THP-1) and macrophages from mice. Infection with L. mexicana or L. major blocked IL-1β release triggered by hemozoin. This depended on the parasite protein GP63: parasites lacking GP63 did not block it. Parasite culture fluid reduced IL-1β release triggered by hemozoin, silica or asbestos, and the effect grew with the dose of fluid. The article does not name the asbestos fiber type. Infection and purified GP63 reduced reactive oxygen species. Infection also disrupted PKC signaling, and GP63 appeared to cut NLRP3 and related proteins. Results were shown mainly as protein blots, without numbers in the text. The authors concluded that Leishmania, through GP63, can significantly inhibit NLRP3 inflammasome function and IL-1β production.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: laboratory (in vitro) experiments on cultured human and mouse immune cells
• Who was studied: PMA-differentiated human THP-1 cells (a cell line) and bone-marrow derived macrophages from 6-week-old C57Bl/6 mice; no human participants
• Exposure: Cells were pre-infected with Leishmania (L. mexicana, L. major, a GP63 knockout and a GP63 rescue strain) or treated with parasite culture fluid, purified GP63, exosomes or secretome. They were then stimulated with NLRP3 activators: hemozoin, silica, asbestos (200 μg/mL each in one experiment), MSU, ATP or linezolid. The asbestos was obtained from Structure Probe, and its fiber type is not stated.
• Main results:
  • In THP-1 cells, pre-infection with L. mexicana and L. major blocked hemozoin-induced IL-1β maturation and release.
  • The inhibition of hemozoin-induced IL-1β depended on the parasite protease GP63.
  • In THP-1 cells, concentrated L. mexicana culture supernatant inhibited IL-1β secretion induced by hemozoin, silica and asbestos, in a dose-dependent manner.
  • In THP-1 cells, purified GP63 and GP63-containing exosome and secretome preparations inhibited IL-1β maturation induced by hemozoin or MSU.
  • In THP-1 cells, Leishmania infection and purified GP63 reduced the production of reactive oxygen species induced by hemozoin or silica.
  • Hemozoin-induced reactive oxygen species and IL-1β production were mediated by PKC. Leishmania infection reduced PKC-dependent phosphorylation.
  • Infection caused cleavage of NLRP3, and this depended on GP63. Pro-IL-1β and TXNIP were also cleaved, but pro-caspase-1 and ASC were not.
  • IL-1β release induced by linezolid, which does not depend on reactive oxygen species, appeared reduced after infection in both mouse and human cells.
• The authors' conclusion: The authors concluded that Leishmania, through its surface metalloprotease GP63, can significantly inhibit NLRP3 inflammasome function and IL-1β production.
• Limitations the authors state:
  • The authors stated they could not rule out that other parasite factors contribute to the inhibition of reactive oxygen species.

Topics

Medical terms in this study, explained in our Lexicon: Macrophage, Cytokine, Reactive Oxygen Species (ROS).

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