Wright Wright posted an update 5 days, 21 hours ago
Despite the knowledge that these receptors are both present in murine liver, little is known about their role during the acute bacterial induced hepatitis as well as their impact in acute liver diseases is not present in the literature yet. We performed a study using the LPS-model to induce an acute liver injury in wild type and constitutive mFPR1- and mFPR2- knockout mice. Afterwards we performed histological, clinical and biochemical analysis of the observed effects in the liver of those animals. Mice were sacrificed 3 h and 6 h post LPS-stimulation, blood and liver were removed and preserved for biochemical and immunohistological assays. After stimulation the mice were kept in SII-long-cages with access to food and water ad libitum. Blood was taken retroorbital before sacrifice of the mice. The serum was separated by centrifugation and stored at 220uC until measurement. All experiments were performed in accordance to the German protection of animals act and with permission of the authority of the federal state North Rhine Westphalia. Formyl peptide receptors 1 and 2 are known to function as important mediators of chemotaxis of hematopoietic cells. The receptors interact with a menagerie of structurally diverse pro- and anti-inflammatory ligands associated with different diseases, including amyloidosis, Alzheimer’s disease, prion disease and HIV. After activation by theirs respective ligands either fMLF or Lipoxin A4, FPRs induce various effects to haematopoietic cells such as chemotaxis or release of superoxide. Furthermore it was shown that deficiency of FPR1 in neutrophils leads to disorientation and inability to migrate to an area of injury e.g. the liver. So far the knowledge about their role in parenchymal liver cells is marginal. For FPR2 it has to be pointed out, that it plays a promiscuous role. On the one hand it can interact with pro-inflammatory ligand such as fMLF and Cramp on the other hand it also interacts with antiinflammatory ligands with seem to have a more prominent effect in activation of FPR2 downstream signalling. Previous work about regulation of liver inflammation after an injury pointed out the importance of maintaining liver homeostasis and to avoid chronic inflammatory liver injury and in the final stages chronic liver diseases. We compared the effect of mFPR1 and mFPR2 deficiency after LPS-stimulation, mimicking a bacterial mediated liver injury. At the later 6 h time point, both, mFPR1-/- and mFPR2-/-, displayed a significantly higher Level of ALT. For AST a slightly different pattern appears. Wild type mice had the highest levels of AST detectable in the serum compared to mFPR1 and mFPR2- deficient mice. 6 h post LPS the mFPR1 and mFPR2 knockout mice displayed significant higher levels of AST in the serum. These findings support a protective role for formyl peptide receptors during progression of LPS induced liver injury. The histological analysis after LPS-stimulation revealed a differential recruitment of immune cells in a time and genotype dependent manner. The cytokine IL-6 is not only known as a recruiting molecule for immune cells. It is described as one of the main drivers of hepatoprotection during liver injury, which mediates hepatoprotection against FAS-induced apoptosis as well as TNF-a induced apoptosis in the liver. The differential expression of IL-6, which is described as one of the most critical regulators of the immune response in the liver suggest, that mFPR1 mediated signalling is involved in the regulation of the early phase of inflammatory response in the liver and as a possible modulator of IL-6 signalling. A similar pattern is shown by the analysis of the expression of CXCL1 which correlates with the IL-6 expression. At the 6h time point increased migration of immune cells to the liver of mFPR1- and mFPR2-deficient mice. The more detailed analysis of those liver infiltrating cells was done by staining FFPE-liver tissues with antibodies for myeoloid cells or neutrophils. In comparison to wild type mice monocytes and neutrophils displayed a stronger presence in the livers of FPR1-/- and FPR2-/- mice 6 h after LPS stimulation. Interestingly mFPR2-/- mice showed a lower tendency regarding the number of Ly6G + – cells visible per view field. The closest explanation for this phenomenon is the link to the neutrophil recruiting cytokine CXCL1 which showed the same tendency at least on mRNA level at 3 h and at 6 h post LPS-stimulation. Differential roles for mFPR1 and mFPR2 regarding immune cell homing is not excluded for granulocytes and supported by the literature. It was shown recently, that FPR1 regulates the antiinflammatory response. Whether this response is correlated to the IL-6 signalling remains to be investigated. A further finding of the regulation of the anti-inflammatory response is visible for other PAMP-receptors such as TLR4 and TLR2. The analysis of theirs expression by qPCR reveals an increment in mFPR1 and mFPR2-deficient animals for TLR2 3 h and 6 h post LPS. TLR4 showed a high expression in WT animals at 3 h and a significantly reduced expression in mFPR1 and mFPR2 deficient mice. On the other hand 6 h post LPS stimulation the TLR4 gene is significantly higher expressed in the mFPR1 and mFPR2-knockout mice. This leads to the conclusion that pathogen recognition might be delayed in the formyl peptide-receptor deficient mice and that both receptors contribute to this recognition and are essential for a stringent and correct procedure of this. This furthermore supports an immunomodulatory function of FPRs, which might not be exclusively provided by hematopoietic cells but also by parenchymal liver cells e.g. hepatocytes and hepatic stellate cells. In contrast to previous publications, the number of apoptotic cells in the liver of mFPR2-/- mice was the highest of all mice strains used in this study.