Endothelial p300 Promotes Portal Hypertension and Hepatic Fibrosis Through C-C Motif Chemokine Ligand 2-Mediated Angiocrine Signaling

Background and Aims During liver fibrosis, liver sinusoidal endothelial cells (LSECs) release angiocrine signals to recruit inflammatory cells into the liver. p300, a master regulator of gene transcription, is associated with pathological inflammatory response. Therefore, we examined how endothelial p300 regulates angiocrine signaling and inflammation related to portal hypertension and fibrogenesis. Approach and Results CCl4 or partial inferior vena cava ligation (pIVCL) was used to induce liver injury. Mice with LSEC-specific p300 deletion (p300(LSEC Delta/Delta)) or C-C motif chemokine ligand 2 (Ccl2) deficiency, nuclear factor kappa B (NF kappa B)-p50 knockout mice, and bromodomain containing 4 (BRD4) inhibitors in wild-type mice were used to investigate mechanisms of inflammation regulation. Leukocytes were analyzed by mass cytometry by time-of-flight. Epigenetic histone marks were modified by CRISPR endonuclease-deficient CRISPR-associated 9-fused with the Kruppel associated box domain (CRISPR-dCas9-KRAB)-mediated epigenome editing. Portal pressure and liver fibrosis were reduced in p300(LSEC Delta/Delta) mice compared to p300(fl/fl) mice following liver injury. Accumulation of macrophages was also reduced in p300(LSEC Delta/Delta) mouse livers. Ccl2 was the most up-regulated chemokine in injured LSECs, but its increase was abrogated in p300(LSEC Delta/Delta) mice. While the macrophage accumulation was increased in NF kappa B-p50 knockout mice with enhanced NF kappa B activity, it was reduced in mice with LSEC-specific Ccl2 deficiency and mice treated with specific BRD4 inhibitors. In vitro, epigenome editing of CCL2 enhancer and promoter regions by CRISPR-dCas9-KRAB technology repressed TNF alpha-induced CCL2 transcription through H3K9 trimethylation. In contrast, TNF alpha activated CCL2 transcription by promoting p300 interaction with NF kappa B and BRD4, leading to histone H3 lysine 27 acetylation at CCL2 enhancer and promoter regions. Conclusions In summary, endothelial p300 interaction with NF kappa B and BRD4 increases CCL2 expression, leading to macrophage accumulation, portal hypertension, and liver fibrosis. Inhibition of p300 and its binding partners might serve as therapy in the treatment of liver diseases.

Automated summary

Deletion of endothelial p300 can alleviate portal hypertension and liver fibrosis caused by liver injury, reducing macrophage accumulation. The regulation of inflammation may be associated with Ccl2, NF kappa B, and BRD4.