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Overexpression of hepatic serum amyloid A1 in mice increases IL-17-producing innate immune cells and decreases bone density.

ABSTRACT: Serum amyloid A (SAA) is an acute-phase protein produced primarily in the liver that plays a key role in both the initiation and maintenance of inflammation. Rapidly secreted SAA induces neutrophilia at inflammatory sites, initiating inflammation and inducing the secretion of various cytokines, including TNF-α, IL-6, and IL-17. IL-17 is expressed in several inflammatory cells, including innate immune cells such as γδT cells, ILC3 cells, and neutrophils. Increased IL-17 levels exacerbate various inflammatory diseases. Among other roles, IL-17 induces bone loss by increasing receptor activator of nuclear factor-κB ligand (RANKL) secretion, which stimulates osteoclast differentiation. Several studies have demonstrated that chronic inflammation induces bone loss, suggesting a role for SAA in bone health. To test this possibility, we observed an increase in IL-17-producing innate immune cells, neutrophils, and γδT cells in these mice. In 6-month-old animals, we detected increased osteoclast-related gene expression and IL-17 expression in bone lysates. We also observed an increase in neutrophils that secreted RANKL in the bone marrow of TG mice. Finally, we demonstrated decreased bone mineral density in these transgenic (TG) mice. Our results revealed that the TG mice have increased populations of IL-17-producing innate immune cells, γδT cells, and neutrophils in TG mice. We additionally detected increased RANKL and IL-17 expression in the bone marrow of 6-month-old TG mice. Furthermore, we confirmed significant increases in RANKL-expressing neutrophils in TG mice and decreased bone mineral density. Our results provide evidence that chronic inflammation induced by SAA1 causes bone loss via IL-17-secreting innate immune cells.

SUBMITTER: Choi M

PROVIDER: S-EPMC8086136 | biostudies-literature | 2021 Jan-Jun

REPOSITORIES: biostudies-literature

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Overexpression of hepatic serum amyloid A1 in mice increases IL-17-producing innate immune cells and decreases bone density.

Choi Minjee M Park Song S Yi Jun Koo JK Kwon Wookbong W Jang Soyoung S Kim Si-Yong SY Yu Wookyung W Kim Myoung Ok MO Ryoo Zae Young ZY Choi Seong-Kyoon SK

The Journal of biological chemistry 20210101

Serum amyloid A (SAA) is an acute-phase protein produced primarily in the liver that plays a key role in both the initiation and maintenance of inflammation. Rapidly secreted SAA induces neutrophilia at inflammatory sites, initiating inflammation and inducing the secretion of various cytokines, including TNF-α, IL-6, and IL-17. IL-17 is expressed in several inflammatory cells, including innate immune cells such as γδT cells, ILC3 cells, and neutrophils. Increased IL-17 levels exacerbate various ...[more]

PMID: 33781747

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Project description:BACKGROUND:IL-17 plays a pathogenic role in asthma. ST2- inflammatory group 2 innate lymphoid cells (ILC2s) driven by IL-25 can produce IL-17, whereas ST2+ natural ILC2s produce little IL-17. OBJECTIVE:We characterized ST2+IL-17+ ILC2s during lung inflammation and determined the pathogenesis and molecular regulation of ST2+IL-17+ ILC2s. METHODS:Lung inflammation was induced by papain or IL-33. IL-17 production by lung ILC2s from wild-type, Rag1-/-, Rorcgfp/gfp, and aryl hydrocarbon receptor (Ahr)-/- mice was examined by using flow cytometry. Bone marrow transfer experiments were performed to evaluate hematopoietic myeloid differentiation primary response gene-88 (MyD88) signaling in regulating IL-17 production by ILC2s. mRNA expression of IL-17 was analyzed in purified naive ILC2s treated with IL-33, leukotrienes, and inhibitors for nuclear factor of activated T cells, p38, c-Jun N-terminal kinase, or nuclear factor κ light-chain enhancer of activated B cells. The pathogenesis of IL-17+ ILC2s was determined by transferring wild-type or Il17-/- ILC2s to Rag2-/-Il2rg-/- mice, which further induced lung inflammation. Finally, expression of 106 ILC2 signature genes was compared between ST2+IL-17+ ILC2s and ST2+IL-17- ILC2s. RESULTS:Papain or IL-33 treatment boosted IL-17 production from ST2+ ILC2s (referred to by us as ILC217s) but not ST2- ILC2s. Ahr, but not retinoic acid receptor-related orphan receptor γt, facilitated the production of IL-17 by ILC217s. The hematopoietic compartment of MyD88 signaling is essential for ILC217 induction. IL-33 works in synergy with leukotrienes, which signal through nuclear factor of activated T-cell activation to promote IL-17 in ILC217s. Il17-/- ILC2s were less pathogenic in lung inflammation. ILC217s concomitantly expressed IL-5 and IL-13 but expressed little GM-CSF. CONCLUSION:During lung inflammation, IL-33 and leukotrienes synergistically induce ILC217s. ILC217s are a highly pathogenic and unexpected source for IL-17 in lung inflammation.

Dataset Information

Overexpression of hepatic serum amyloid A1 in mice increases IL-17-producing innate immune cells and decreases bone density.

Publications

Overexpression of hepatic serum amyloid A1 in mice increases IL-17-producing innate immune cells and decreases bone density.

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