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Analyzing the Functions of Mast Cells In Vivo Using 'Mast Cell Knock-in' Mice
Published on: May 27, 2015
Bacterial DNA promoting inflammation via the Sgk1/Nedd4L/Syk pathway in mast cells contributes to
Bangtao Chen1, Yao Song2,3, Xiongbo Yang1
1Department of Dermatology, Chongqing University Three Gorges Hospital, School of Medicine, Chongqing University, No.165, Xincheng Road, Wanzhou District, Chongqing 400030, China.
Abstract:
Inflammation centered on non-IgE-mediated mast cell activation characterizes chronic spontaneous urticaria resistant to nonsedating H1-antihistamines. We recently uncovered a strong positive association between inflammation and the fecal Escherichia. To further explore the actions of bacterial DNA derived from Escherichia on mast cells, intestinal permeability of patients with chronic spontaneous urticaria with or without nonsedating H1-antihistamine resistance and healthy controls were determined, and LAD2 cells with knockdown of Syk, Nedd4L, or Sgk1 or with incubation of inhibitors GS9973, GSK650394, and MG132 were posttreated with btDNA. We found that (i) serum intestinal permeability indices and bacterial DNA markedly increased in patients with chronic spontaneous urticaria with nonsedating H1-antihistamine resistance compared with those without (all P < 0.001), and bacterial DNA positively correlated with the degree of inflammation; (ii) IL-6 and TNF-α levels were time- and dose-dependently upregulated in bacterial DNA-stimulated LAD2 cells, which relied on unmethylated CpG in bacterial DNA and Toll-like receptor 9 protein in cells; (iii) Syk knockdown or inhibition of Syk Tyr525/526 phosphorylation blocked bacterial DNA-initiated cytokine production; (iv) Nedd4L interacted with Tyr525/526-phosphorylated Syk, and inhibition of Nedd4L Ser448 phosphorylation induced by bacterial DNA-activated Sgk1 was mandatory for bacterial DNA's proinflammatory property; and (v) Sgk1 suppression showed an inhibitory effect on bacterial DNA-induced inflammation by ensuring Nedd4L-mediated ubiquitination of Tyr525/526-phosphorylated Syk. Collectively, we identified previously unknown contributory roles of bacterial translocation and serum bacterial DNA on the inflammation phenotype in patients with chronic spontaneous urticaria with nonsedating H1-antihistamine resistance and further uncovered a vital negative regulatory role for the Sgk1/Nedd4L/Syk pathway in bacterial DNA-induced inflammation in LAD2 cells.
Insights
Bacterial DNA translocation contributes to inflammation in chronic spontaneous urticaria resistant to antihistamines. A key Sgk1/Nedd4L/Syk pathway negatively regulates this bacterial DNA-induced mast cell inflammation.
Area of Science:
- Immunology
- Dermatology
- Microbiology
Background:
- Chronic spontaneous urticaria (CSU) resistant to antihistamines involves non-IgE-mediated mast cell activation.
- A link between inflammation and fecal Escherichia was previously observed in CSU patients.
Purpose of the Study:
- To investigate the role of bacterial DNA from Escherichia in mast cell activation and inflammation in CSU.
- To explore the intestinal permeability and serum bacterial DNA levels in CSU patients with and without antihistamine resistance.
Main Methods:
- Measured intestinal permeability and serum bacterial DNA in CSU patients and controls.
- Stimulated LAD2 mast cells with bacterial DNA (btDNA) and analyzed cytokine production (IL-6, TNF-α).
- Utilized gene knockdown (Syk, Nedd4L, Sgk1) and pharmacological inhibitors to dissect signaling pathways.
Main Results:
- Increased intestinal permeability and serum bacterial DNA in antihistamine-resistant CSU patients, correlating with inflammation.
- Bacterial DNA upregulated IL-6 and TNF-α in LAD2 cells via Toll-like receptor 9 (TLR9).
- The Sgk1/Nedd4L/Syk pathway was identified as a negative regulator of bacterial DNA-induced mast cell inflammation.
Conclusions:
- Bacterial translocation and serum bacterial DNA are implicated in antihistamine-resistant CSU inflammation.
- The Sgk1/Nedd4L/Syk pathway plays a critical role in modulating mast cell responses to bacterial DNA.
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