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Macrophages monitor tissue osmolarity and induce inflammatory response through NLRP3 and NLRC4 inflammasome activation.

Ip WK, Medzhitov R - Nat Commun (2015)

Bottom Line: Mammalian cells have effective mechanisms to cope with osmotic stress by engaging various adaptation responses.Mice with high dietary salt intake display enhanced induction of Th17 response upon immunization, and this effect is abolished in caspase-1-deficient mice.Our findings identify an unknown function of the inflammasome as a sensor of hyperosmotic stress, which is crucial for the induction of inflammatory Th17 response.

View Article: PubMed Central - PubMed

Affiliation: Howard Hughes Medical Institute, Department of Immunobiology, Yale University School of Medicine, New Haven, Connecticut 06520, USA.

ABSTRACT
Interstitial osmolality is a key homeostatic variable that varies depending on the tissue microenvironment. Mammalian cells have effective mechanisms to cope with osmotic stress by engaging various adaptation responses. Hyperosmolality due to high dietary salt intake has been linked to pathological inflammatory conditions. Little is known about the mechanisms of sensing the hyperosmotic stress by the innate immune system. Here we report that caspase-1 is activated in macrophages under hypertonic conditions. Mice with high dietary salt intake display enhanced induction of Th17 response upon immunization, and this effect is abolished in caspase-1-deficient mice. Our findings identify an unknown function of the inflammasome as a sensor of hyperosmotic stress, which is crucial for the induction of inflammatory Th17 response.

No MeSH data available.


Related in: MedlinePlus

Hyperosmotic stress induces IL-1β secretion in macrophages (a) BMDMs primed without (PBS) or with LPS were incubated overnight in isotonic conditions (control) or hyperosmotic conditions (+ 200 mOsm) by adding NaCl, glucose, or sorbitol, or stimulated with ATP (5 mM) or alum (250 μg/ml) for 2 h or 6 h respectively. IL-1β, IL-1α and IL-6 in media supernatants were measured by ELISA. (b, c) Wild-type (C57BL/6) or IL-1R-deficient mice (IL-1R KO) were injected peritoneally with 0.15 M (“isotonic”) or 0.35 M (“hypertonic”) of NaCl (each group, n = 4). Peritoneal lavage cells were analyzed for neutrophils after 16 h. Contour plots of FACS analysis show the percentages of neutrophils (Ly-6G+, F4/80 negative), inflammatory monocytes (Ly-6G+, F4/80+low), and resident macrophages (Ly-6G negative, F4/80+high) cells (b). Neutrophil numbers were determined by using cell-counting beads as described in the Methods (c). Data are representative of three (a, b) independent experiments. Data indicate mean ± s.d. of quadruplicates (a), or for pooled groups of mice from three experiments (c). Student’s t test: *, P ≤ 0.05.
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Figure 2: Hyperosmotic stress induces IL-1β secretion in macrophages (a) BMDMs primed without (PBS) or with LPS were incubated overnight in isotonic conditions (control) or hyperosmotic conditions (+ 200 mOsm) by adding NaCl, glucose, or sorbitol, or stimulated with ATP (5 mM) or alum (250 μg/ml) for 2 h or 6 h respectively. IL-1β, IL-1α and IL-6 in media supernatants were measured by ELISA. (b, c) Wild-type (C57BL/6) or IL-1R-deficient mice (IL-1R KO) were injected peritoneally with 0.15 M (“isotonic”) or 0.35 M (“hypertonic”) of NaCl (each group, n = 4). Peritoneal lavage cells were analyzed for neutrophils after 16 h. Contour plots of FACS analysis show the percentages of neutrophils (Ly-6G+, F4/80 negative), inflammatory monocytes (Ly-6G+, F4/80+low), and resident macrophages (Ly-6G negative, F4/80+high) cells (b). Neutrophil numbers were determined by using cell-counting beads as described in the Methods (c). Data are representative of three (a, b) independent experiments. Data indicate mean ± s.d. of quadruplicates (a), or for pooled groups of mice from three experiments (c). Student’s t test: *, P ≤ 0.05.

Mentions: To examine whether the inflammasome is activated by hyperosmotic stress, BMDMs were exposed to hypertonic conditions after priming with LPS to allow the expression of pro-IL-1β. There was no IL-1β or IL-6 secretion observed in non-primed BMDMs (Fig. 2a). However, after LPS priming, IL-1β secretion was induced in BMDMs incubated in hypertonic conditions with NaCl or glucose, whereas IL-6 secretion was observed in both isotonic and hypertonic conditions (Fig. 2a), suggesting that hyperosmotic stress induces the processing and release of mature IL-1β. Notably, the secretion of IL-1β by hypertonic stress was at a lower range as compared with that by the known inflammasome-activating agents such as ATP and alum (Fig. 2a). Similar results were also observed in macrophage cell line J774 (Supplementary Fig. 1). Moreover, hyperosmotic stress also induced the release of IL-1α (Fig. 2a), which, like IL-1β, has been shown to rely on caspase-1 activity 29.


Macrophages monitor tissue osmolarity and induce inflammatory response through NLRP3 and NLRC4 inflammasome activation.

Ip WK, Medzhitov R - Nat Commun (2015)

Hyperosmotic stress induces IL-1β secretion in macrophages (a) BMDMs primed without (PBS) or with LPS were incubated overnight in isotonic conditions (control) or hyperosmotic conditions (+ 200 mOsm) by adding NaCl, glucose, or sorbitol, or stimulated with ATP (5 mM) or alum (250 μg/ml) for 2 h or 6 h respectively. IL-1β, IL-1α and IL-6 in media supernatants were measured by ELISA. (b, c) Wild-type (C57BL/6) or IL-1R-deficient mice (IL-1R KO) were injected peritoneally with 0.15 M (“isotonic”) or 0.35 M (“hypertonic”) of NaCl (each group, n = 4). Peritoneal lavage cells were analyzed for neutrophils after 16 h. Contour plots of FACS analysis show the percentages of neutrophils (Ly-6G+, F4/80 negative), inflammatory monocytes (Ly-6G+, F4/80+low), and resident macrophages (Ly-6G negative, F4/80+high) cells (b). Neutrophil numbers were determined by using cell-counting beads as described in the Methods (c). Data are representative of three (a, b) independent experiments. Data indicate mean ± s.d. of quadruplicates (a), or for pooled groups of mice from three experiments (c). Student’s t test: *, P ≤ 0.05.
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Figure 2: Hyperosmotic stress induces IL-1β secretion in macrophages (a) BMDMs primed without (PBS) or with LPS were incubated overnight in isotonic conditions (control) or hyperosmotic conditions (+ 200 mOsm) by adding NaCl, glucose, or sorbitol, or stimulated with ATP (5 mM) or alum (250 μg/ml) for 2 h or 6 h respectively. IL-1β, IL-1α and IL-6 in media supernatants were measured by ELISA. (b, c) Wild-type (C57BL/6) or IL-1R-deficient mice (IL-1R KO) were injected peritoneally with 0.15 M (“isotonic”) or 0.35 M (“hypertonic”) of NaCl (each group, n = 4). Peritoneal lavage cells were analyzed for neutrophils after 16 h. Contour plots of FACS analysis show the percentages of neutrophils (Ly-6G+, F4/80 negative), inflammatory monocytes (Ly-6G+, F4/80+low), and resident macrophages (Ly-6G negative, F4/80+high) cells (b). Neutrophil numbers were determined by using cell-counting beads as described in the Methods (c). Data are representative of three (a, b) independent experiments. Data indicate mean ± s.d. of quadruplicates (a), or for pooled groups of mice from three experiments (c). Student’s t test: *, P ≤ 0.05.
Mentions: To examine whether the inflammasome is activated by hyperosmotic stress, BMDMs were exposed to hypertonic conditions after priming with LPS to allow the expression of pro-IL-1β. There was no IL-1β or IL-6 secretion observed in non-primed BMDMs (Fig. 2a). However, after LPS priming, IL-1β secretion was induced in BMDMs incubated in hypertonic conditions with NaCl or glucose, whereas IL-6 secretion was observed in both isotonic and hypertonic conditions (Fig. 2a), suggesting that hyperosmotic stress induces the processing and release of mature IL-1β. Notably, the secretion of IL-1β by hypertonic stress was at a lower range as compared with that by the known inflammasome-activating agents such as ATP and alum (Fig. 2a). Similar results were also observed in macrophage cell line J774 (Supplementary Fig. 1). Moreover, hyperosmotic stress also induced the release of IL-1α (Fig. 2a), which, like IL-1β, has been shown to rely on caspase-1 activity 29.

Bottom Line: Mammalian cells have effective mechanisms to cope with osmotic stress by engaging various adaptation responses.Mice with high dietary salt intake display enhanced induction of Th17 response upon immunization, and this effect is abolished in caspase-1-deficient mice.Our findings identify an unknown function of the inflammasome as a sensor of hyperosmotic stress, which is crucial for the induction of inflammatory Th17 response.

View Article: PubMed Central - PubMed

Affiliation: Howard Hughes Medical Institute, Department of Immunobiology, Yale University School of Medicine, New Haven, Connecticut 06520, USA.

ABSTRACT
Interstitial osmolality is a key homeostatic variable that varies depending on the tissue microenvironment. Mammalian cells have effective mechanisms to cope with osmotic stress by engaging various adaptation responses. Hyperosmolality due to high dietary salt intake has been linked to pathological inflammatory conditions. Little is known about the mechanisms of sensing the hyperosmotic stress by the innate immune system. Here we report that caspase-1 is activated in macrophages under hypertonic conditions. Mice with high dietary salt intake display enhanced induction of Th17 response upon immunization, and this effect is abolished in caspase-1-deficient mice. Our findings identify an unknown function of the inflammasome as a sensor of hyperosmotic stress, which is crucial for the induction of inflammatory Th17 response.

No MeSH data available.


Related in: MedlinePlus