Early and late phases of liver sinusoidal endothelial cell (LSEC) defenestration in mouse model of systemic inflammation

BACKGROUND

Liver sinusoidal endothelial cells (LSECs) have transcellular pores, called fenestrations, participating in the bidirectional transport between the vascular system and liver parenchyma. Fenestrated LSECs indicate a healthy phenotype of liver while loss of fenestrations (defenestration) in LSECs is associated with liver pathologies.

METHODS

We introduce a unique model of systemic inflammation triggered by the deletion of Mcpip1 in myeloid leukocytes (Mcpip1fl/flLysMCre) characterised by progressive alterations in LSEC phenotype. We implement multiparametric characterisation of LSECs by using novel real-time atomic force microscopy supported with scanning electron microscopy and quantitative fluorescence microscopy. In addition, we provide genetic profiling, searching for characteristic genes encoding proteins that might be connected with the structure of fenestrations.

RESULTS

We demonstrate that LSECs in Mcpip1fl/flLysMCre display two phases of defenestration: the early phase, with modest defenestration that was fully reversible using cytochalasin B and the late phase, with severe defenestration that is mostly irreversible. By thorough analysis of LSEC porosity, elastic modulus and actin abundance in Mcpip1fl/flLysMCre and in response to cytochalasin B, we demonstrate that proteins other than actin must be additionally responsible for inducing open fenestrations. We highlight several genes that were severely affected in the late but not in the early phase of LSEC defenestration shedding a light on complex structure of individual fenestrations.

CONCLUSIONS

The presented model of LSEC derived from Mcpip1fl/flLysMCre provides a valuable reference for developing novel strategies for LSEC refenestration in the early and late phases of liver pathology.

Diosmetin alleviates TNFα-induced liver inflammation by improving liver sinusoidal endothelial cell dysfunction

Sterile inflammation contributes to the development of many liver diseases including non-alcoholic fatty liver disease. Tumor necrosis factor alpha (TNFα) is a key cytokine driving liver inflammation primarily through pro-inflammatory activation of liver sinusoidal endothelial cells (LSEC). The knowledge of whether modulating LSEC activation can alleviate liver inflammation is scarce. This study aims to establish and validate an animal model mimicking LSEC dysfunction observed in obese patients with elevated plasma levels of TNFα, and explore whether vasoactive flavonoid diosmetin could serve as a therapeutic agent for liver inflammation by modulation of LSEC dysfunction. Obese patients with elevated plasma levels of TNFα, LSEC dysfunction and liver inflammation had also reduced Mcpip1 expression in peripheral blood mononuclear cells. Mcpip1 is a protein that negatively regulates the levels of pro-inflammatory cytokines. To model this, we generated mice with Mcpip1 knock-out in myeloid cells (Mcpip1fl/flLysMCre), which displayed systemic and liver inflammation like that observed in patients. Diosmetin treatment efficiently reduced TNFα-dependent LSEC activation in vitro and in vivo, and reduced liver inflammation in Mcpip1fl/flLysMCre mice without affecting systemic inflammation. Diosmetin's effects may stem from inhibiting NF-κB pathway in TNFα-activated endothelial cells. Our findings demonstrate that the Mcpip1fl/flLysMCre mouse model is useful for studying new anti-inflammatory therapies for the liver. We show that diosmetin, a vasoactive flavonoid used in the clinic to treat chronic venous insufficiency, also has strong anti-inflammatory properties in the liver. These results indicate that diosmetin has the potential to be further investigated as a supportive therapy for liver inflammation in humans.