Arthritis & Rheumatism, Volume 62,
November 2010 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Atlanta, Georgia November 6-11, 2010.


The NALP3 Inflammasome Is Activated by Sodium Overload and Water Influx in Gouty Arthritis.

Schorn1,  Christine, Frey2,  Benjamin, Janko1,  Christina, Schett3,  Georg, Herrmann1,  Martin

Department of Internal Medicine III and Institute for Clinical Immunology, University of Erlangen-Nuremberg, Erlangen, Germany
Department of Radiation Oncology, Friedrich-Alexander University of Erlangen-Nuremberg, Erlangen, Germany
Friedrich Alexander Univ, Erlangen, Germany

Background:

One of the endogenous danger molecules of dying cells generated during apoptosis is monosodium urate (MSU). Precipitated MSU crystals in tissues and joints induce an inflammatory process with IL-1b induction after NALP3 inflammasome activation resulting in gouty arthritis. However, the exact mechanism of NALP3 activation is still elusive.

Purpose:

Identification of the mechanism of NALP3 inflammasome dependent IL-1b production induced by MSU crystals.

Methods:

The uptake of MSU was analysed by time lapse microscopy and cytofluorometry. The plasma membrane integrity after ingestion of MSU was investigated by propidium iodide staining. Via REM-EDX the morphological and chemical structure of urate crystals was identified. The relative intracellular sodium concentration was analysed by Sodium Green fluorescence. The human IL-1b induction in presence of inhibitors of lysosomal acidification and of aquaporins in culture supernatants was quantified by simplex bead technology. Additionally, in an in vivo mice experiment animals were treated i.p. with chloroquine following injection of MSU in generated air pouches. The IL-1b production in the pouch fluid was quantified by ELISA.

Results:

Blood borne phagocytes ingest MSU crystals and substantially increase their side scatter (SSc) reflecting increased "granularity". After the uptake of the crystals the cells swell shown by augmented forward scatter (FSc) and time lapse microscopy. Most of the phagocytes show an intact plasma membrane after ingestion of crystals. The treatment of phagocytes with MSU results in an induction of IL-1b production. Needle-shaped MSU crystals release sodium after treatment with acidic milieu and switch into barrel-shaped crystals. In swollen cells the intracellular sodium concentration of phagocytes after the uptake of MSU displays a markedly increased intracellular sodium concentration. Furthermore, the inhibition of lysosomal acidification and of aquaporins results in reduction of IL-1b production in in vitro and in vivo.

Conclusion(s):

We suggest a novel model of NALP3 inflammasome activation after phagocytosis of MSU crystals: the phagocytes ingest crystals into endosomes resulting in fusion with acidic lysosomes. That induces a massive release of sodium from the MSU crystal and enhances the intracellular osmolarity. The hyperosmolarity of the cell is compensated by passive water influx through aquaporins following cell swelling. The latter reduces the intracellular potassium concentration below the threshold of NALP3 inflammasome activation. Finally, the decreased IL-1b production by treatment with inhibitors of lysosomal acidification or inhibitors of aquaporins supports our new model of inflammasome activation by MSU.

To cite this abstract, please use the following information:
Schorn, Christine, Frey, Benjamin, Janko, Christina, Schett, Georg, Herrmann, Martin; The NALP3 Inflammasome Is Activated by Sodium Overload and Water Influx in Gouty Arthritis. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :2150
DOI: 10.1002/art.29914

Abstract Supplement

Meeting Menu

2010 ACR/ARHP