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TLR3 agonists induce fibronectin aggregation by activated astrocytes: a role of pro-inflammatory cytokines and fibronectin splice variants.

ABSTRACT: Multiple sclerosis (MS) is a chronic demyelinating disease of the central nervous system which eventually results in axonal loss mainly due to failure of remyelination. Previously we have shown that the persistent presence of stable astrocyte-derived fibronectin aggregates in MS lesions impairs OPC differentiation, and thereby remyelination. Here we set out to discern whether and, if so, how inflammatory mediators as present in MS lesions trigger astrocytes to form fibronectin aggregates. Our findings revealed that in slice cultures only upon demyelination, the TLR3 agonist Poly(I:C) evoked astrocytes to form fibronectin aggregates. Consistently, pro-inflammatory cytokine-pretreated astrocytes were more susceptible to Poly(I:C)-induced fibronectin aggregation, indicating that astrocytes form fibronectin aggregates upon a double hit by inflammatory mediators. The underlying mechanism involves disrupted fibronectin fibrillogenesis at the cell surface as a result of a cytokine-induced increase in relative mRNA levels of EIIIApos-Fn over EIIIBpos-Fn and a Poly(I:C)-mediated decrease in integrin affinity. Remarkably, fibronectin aggregation is exacerbated by white matter astrocytes compared to grey matter astrocytes, which may be a reflection of higher expression levels of EIIIApos-fibronectin in white matter astrocytes. Hence, interfering with alternative fibronectin splicing and/or TLR3-mediated signaling may prevent fibronectin aggregation and overcome remyelination failure in MS lesions.

SUBMITTER: Werkman I

PROVIDER: S-EPMC6969115 | biostudies-literature | 2020 Jan

REPOSITORIES: biostudies-literature

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TLR3 agonists induce fibronectin aggregation by activated astrocytes: a role of pro-inflammatory cytokines and fibronectin splice variants.

Werkman Inge I Sikkema Arend H AH Versluijs Joris B JB Qin Jing J de Boer Pascal P Baron Wia W

Scientific reports 20200117 1

Multiple sclerosis (MS) is a chronic demyelinating disease of the central nervous system which eventually results in axonal loss mainly due to failure of remyelination. Previously we have shown that the persistent presence of stable astrocyte-derived fibronectin aggregates in MS lesions impairs OPC differentiation, and thereby remyelination. Here we set out to discern whether and, if so, how inflammatory mediators as present in MS lesions trigger astrocytes to form fibronectin aggregates. Our fi ...[more]

PMID: 31953424

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Project description:BACKGROUND:Astrocytes contribute to the crosstalk that generates chronic neuro-inflammation in neurological diseases; however, compared with microglia, astrocytes respond to a more limited continuum of innate immune system stimulants. Recent studies suggest that the fibrinolysis system may regulate inflammation. The goal of this study was to test whether fibrinolysis system components activate astrocytes and if so, elucidate the responsible biochemical pathway. METHODS:Primary cultures of astrocytes and microglia were prepared from neonatal mouse brains. The ability of purified fibrinolysis system proteins to elicit a pro-inflammatory response was determined by measuring expression of the mRNAs encoding tumor necrosis factor-? (TNF-?), interleukin-1? (IL-1?), and chemokine (C-C motif) ligand 2 (CCL2). I?B? phosphorylation also was measured. Plasminogen activation in association with cells was detected by chromogenic substrate hydrolysis. The activity of specific receptors was tested using neutralizing antibodies and reagents. RESULTS:Astrocytes expressed pro-inflammatory cytokines when treated with plasminogen but not when treated with agonists for Toll-like Receptor-4 (TLR4), TLR2, or TLR9. Microglia also expressed pro-inflammatory cytokines in response to plasminogen; however, in these cells, the response was observed only when tissue-type plasminogen activator (tPA) was added to activate plasminogen. In astrocytes, endogenously produced urokinase-type plasminogen activator (uPA) converted plasminogen into plasmin in the absence of tPA. Plasminogen activation was dependent on the plasminogen receptor, ?-enolase, and the uPA receptor, uPAR. Although uPAR is capable of directly activating cell-signaling, the receptor responsible for cytokine expression and I?B? phosphorylation response to plasmin was Protease-activated Receptor-1 (PAR-1). The pathway, by which plasminogen induced astrocyte activation, was blocked by inhibiting any one of the three receptors implicated in this pathway with reagents such as ?ACA, ?-enolase-specific antibody, uPAR-specific antibody, the uPA amino terminal fragment, or a pharmacologic PAR-1 inhibitor. CONCLUSIONS:Plasminogen may activate astrocytes for pro-inflammatory cytokine expression through the concerted action of at least three distinct fibrinolysis protease receptors. The pathway is dependent on uPA to activate plasminogen, which is expressed endogenously by astrocytes in culture but also may be provided by other cells in the astrocytic cell microenvironment in the CNS.

Project description:BackgroundAdult human pancreatic beta cells are the "gold standard" for studies on diabetes pathogenesis, but their use is limited by insufficient availability and variable quality. An important effort has recently taken place to differentiate beta cells from human induced pluripotent stem cells (iPSCs) and validate their use for diabetes research. We presently used a 7-stage protocol to generate beta cells from human iPSC and evaluated whether these cells are responsive to the pro-inflammatory cytokines (IFN?, IL-1?, or IFN?) that play a role in type 1 diabetes.MethodsThe iPSC-derived islet-like cell clusters contained 40-50% beta and 10-15% alpha cells and expressed the receptors for IFN?, IL-1?, or IFN?. Cells were exposed to either IFN? (1000?U/mL)?+?IL-1? (50?U/mL) or IFN? alone (2000?U/mL) for 24/48?h. Apoptosis was quantified using Hoechst/propidium iodide staining or the RealTime Glo Apoptosis Kit (Promega). After treatment, CXCL10 secretion was quantified by ELISA. The expression of multiples genes (Ins, Gcg, Nkx2.2, Nkx6.1, Pdx1, Mafa, BiP, Chop, Atf3, CXCL10, CXCL9, CCL5, and HLA-ABC) was quantified by RT-qPCR. Phosphorylation state and total expression of STAT1/STAT2, as well as expression of PDL1 and of the ER chaperone BiP, were quantified by Western blotting. The co-localization of HLA-ABC or cleaved caspase-3 and Ins/Gcg expression was assessed by immunohistochemistry. The presence of HLA-ABC at the plasma membrane was measured by flow cytometry.ResultsIFN? + IL-1? and IFN? induced apoptosis of the cells after 48?h of exposure. Cleaved caspase-3 co-localized mostly but not exclusively with Ins+ cells. Exposure to IFN? + IL-1? induced a pro-inflammatory phenotype, including increased CXCL10, CXCL9, and CCL5 expression; CXCL10 secretion; and HLA-ABC expression. HLA overexpression was confirmed at the protein level by Western blotting and flow cytometry. Exposure to IFN? + IL-1? (but not IFN?) also induced beta cell dedifferentiation and endoplasmic reticulum stress (increase in BiP, Chop, and Atf3 mRNA expression). Phosphorylation of STAT1 was stimulated already after 1?h by IFN? + IL-1? and IFN?, while phosphorylation of STAT2 was only activated by IFN? at 1-4 h. PDL1 expression was increased by both IFN? + IL-1? and IFN?.ConclusionsOur data show that human iPSC-derived beta cells respond to pro-inflammatory cytokines IL-1? + IFN? and IFN?, by activating the same pathogenic processes as adult human primary beta cells. These cells thus represent a valuable tool for future research on the pathogenesis of type 1 diabetes.

Dataset Information

TLR3 agonists induce fibronectin aggregation by activated astrocytes: a role of pro-inflammatory cytokines and fibronectin splice variants.

Publications

TLR3 agonists induce fibronectin aggregation by activated astrocytes: a role of pro-inflammatory cytokines and fibronectin splice variants.

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