Mincle/Syk Signalling Promotes Intestinal Mucosal Inflammation Through Induction of Macrophage Pyroptosis in Crohn's Disease.

BACKGROUND: Macrophage-inducible C-type lectin [Mincle] signalling plays a proinflammatory role in different organs such as the brain and liver, but its role in intestinal inflammation, including Crohn's disease [CD], remains unknown. METHODS: The characteristics of Mincle signalling expression in CD patients and experimental colitis were examined. The functional role of Mincle signalling in the intestine was addressed in experimental colitis models in vivo by using Mincle knock-out [Mincle-/-] mice. In addition, neutralising anti-Mincle antibody, downstream spleen tyrosine kinase [Syk] inhibitor, and Mincle pharmacological agonist were used to study the Mincle signalling in intestine. Bone marrow-derived macrophages were collected from mice and used to further verify the effect of Mincle signalling in macrophages. RESULTS: This study has shown that Mincle signalling was significantly elevated in active human CD and experimental colitis, and macrophages were the principal leukocyte subset that upregulate Mincle signalling. Mincle deficiency and Syk pharmacological inhibition ameliorated the colitis by reducing induced macrophage pyroptosis, and activation of Mincle with the agonist aggravated the intestinal inflammation. The ex vivo studies demonstrated that activation of Mincle signalling promoted the release of proinflammatory cytokines, whereas its absence restricted release of proinflammatory cytokines from pyroptosis of macrophages. In addition, Mincle/Syk signalling in macrophages could promote the production of chemokines to recruit neutrophils by activating mitogen-activated protein kinase [MAPK] during intestinal inflammation. CONCLUSIONS: Mincle signalling promotes intestinal mucosal inflammation by inducing macrophage pyroptosis. Modulation of the Mincle/Syk axis emerges as a potential therapeutic strategy to target inflammation and treat CD.

In vitro and in vivo study of the expression of the Syk/Ras/c­Fos pathway in chronic glomerulonephritis.

Chronic glomerulonephritis (CGN) is the most common form of glomerular disease; however, its associated molecular mechanisms remain unclear. Spleen tyrosine kinase (Syk) is a key mediator of B­receptor signaling on the surface of inflammatory cells. The primary target for R406 is Syk. The aim of the present study was to investigate the molecular mechanisms involved in a rat model of CGN induced by adriamycin (ADR) and in the rat glomerular mesangial cell line, HBZY­1, stimulated by lipopolysaccharide (LPS). CGN was induced in the rat models by two intravenous injections of ADR into the tail: 3.5 mg/kg ADR was given on the first day and 3.0 mg/kg on the fourteenth day. HBZY­1 cells were incubated with 0.5 µg/ml LPS for 48 h. The pathological alterations in the kidney tissues were observed by hematoxylin and eosin staining. The 24 h urinary protein, blood urea nitrogen (BUN) and creatinine levels were measured using an automatic biochemistry analyzer. The mRNA expression levels of Syk, Ras, mitogen activated protein kinase kinase (MEK), extracellular signal regulated kinase (ERK)1/2 and c­Fos was measured by reverse transcription­quantitative polymerase chain reaction. Subsequently, the protein levels of phosphorylated (p)­Syk, Ras, p­MEK1/2, p­ERK1/2 and c­Fos were measured by western blot analysis. In the model group, 24 h urinary protein, BUN and creatinine levels were increased when compared with the normal group (P<0.05). In addition, compared with the normal group, the mRNA and protein levels of the Syk/Ras/c­Fos pathway components in vitro and in vivo were markedly increased, inhibiting the abnormal cell viability of mesangial cells. In conclusion, the results of the present study suggested a potential role for the Syk/Ras/c­Fos signaling pathway in CGN, which indicated the necessity for further investigation at the clinical level.

Secreted IgM deficiency leads to increased BCR signaling that results in abnormal splenic B cell development.

Mice lacking secreted IgM (sIgM -/-) antibodies display abnormal splenic B cell development, which results in increased marginal zone and decreased follicular B cell numbers. However, the mechanism by which sIgM exhibit this effect is unknown. Here, we demonstrate that B cells in sIgM -/- mice display increased B cell receptor (BCR) signaling as judged by increased levels of phosphorylated Bruton's tyrosine kinase (pBtk), phosphorylated Spleen tyrosine kinase (pSyk), and nuclear receptor Nur77. Low dosage treatment with the pBtk inhibitor Ibrutinib reversed the altered B cell development in the spleen of sIgM -/- mice, suggesting that sIgM regulate splenic B cell differentiation by decreasing BCR signaling. Mechanistically, we show that B cells, which express BCRs specific to hen egg lysozyme (HEL) display diminished responsiveness to HEL stimulation in presence of soluble anti-HEL IgM antibodies. Our data identify sIgM as negative regulators of BCR signaling and suggest that they can act as decoy receptors for self-antigens that are recognized by membrane bound BCRs.

The Activating C-type Lectin-like Receptor NKp65 Signals through a Hemi-immunoreceptor Tyrosine-based Activation Motif (hemITAM) and Spleen Tyrosine Kinase (Syk).

NKp65 is an activating human C-type lectin-like receptor (CTLR) triggering cellular cytotoxicity and cytokine secretion upon high-affinity interaction with the cognate CTLR keratinocyte-associated C-type lectin (KACL) selectively expressed by human keratinocytes. Previously, we demonstrated that NKp65-mediated cellular cytotoxicity depends on tyrosine 7, located in a cytoplasmic sequence motif of NKp65 resembling a hemi-immunoreceptor tyrosine-based activation motif (hemITAM). HemITAMs have been reported for a few activating myeloid-specific CTLRs, including Dectin-1 and CLEC-2, and consist of a single tyrosine signaling unit preceded by a triacidic motif. Upon receptor engagement, the hemITAM undergoes phosphotyrosinylation and specifically recruits spleen tyrosine kinase (Syk), initiating cellular activation. In this study, we addressed the functionality of the putative hemITAM of NKp65. We show that NKp65 forms homodimers and is phosphorylated at the hemITAM-embedded tyrosine 7 upon engagement by antibodies or KACL homodimers. HemITAM phosphotyrosinylation initiates a signaling pathway involving and depending on Syk, leading to cellular activation and natural killer (NK) cell degranulation. However, although NKp65 utilizes Syk for NK cell activation, a physical association of Syk with the NKp65 hemITAM could not be detected, unlike shown previously for the hemITAM of myeloid CTLR. Failure of NKp65 to recruit Syk is not due to an alteration of the triacidic motif, which rather affects the efficiency of hemITAM phosphotyrosinylation. In summary, NKp65 utilizes a hemITAM-like motif for cellular activation that requires Syk, although Syk appears not to be recruited to NKp65.

Involvement of syk and VEGF-C in invasion of lung adenocarcinoma A549 cells.

BACKGROUND AND AIMS: Lung cancer has become one of the most dangerous malignant tumors in the world nowadays, whose pathogenesis is complex involving multi-genes and multi-elements. This study aims to investigate the values of spleen tyrosine kinase (Syk) and vascular endothelial growth factor-C (VEGF-C) in lymphangiogenesis and metastasis of lung adenocarcinoma A549 cells. MATERIALS AND METHODS: The pcDNA3.1-VEGF-C and pLNCX-syk were constructed and transfected into A549 cells. After cells with stable expression were sorted, the level of VEGF-C was tested by RT-PCR and immunohistochemistry and the mRNA of syk was tested by RT-PCR. The cell invasion assay was investigated by transwell chamber in vitro. Restriction enzyme digestion and gel electrophoresis demonstrated successful construction of the pcDNA3.1-VEGF-C. RESULTS: RT-PCR and immunohistochemistry revealed higher expression of VEGF-C in VEGFC-construct-transfected A549 cells than that in controls (P < 0.05). Successful construction of the pLNCX-syk was demonstrated by restriction enzyme electrophoresis and sequencing. RT-PCR revealed Syk expression higher in syk-construct-transfected cells than in controls (P < 0.05). CONCLUSIONS: The results indicate a potential link between the upregulation of Syk and VEGF-C expression and lung adenocarcinoma.