Epigenetic regulators in ALD

Alcohol-associated liver disease (ALD) is a major cause of alcohol-related mortality. The specific mechanisms responsible for ALD development and progression are not fully understood, and there is limited therapy for any stage of ALD. Recent advances in single cell sequencing revealed the complex nature of the disease, particularly the importance of cell-cell communication. Using single cell sequencing and co-culture experiments we found that alcohol promotes pathological changes in cell-cell communication in the liver. These changes are in turn mediated by alcohol-related epigenetic changes in hepatocytes, induced by histone modification enzymes called KDM5B and KDM5C.

Preliminary data suggest that KDM5 demethylases are involved in both ALD development and resolution. During disease development, KDM5 demethylases in hepatocytes promote pro-inflammatory and pro-fibrotic signaling in non-parenchymal cells (NPC). During disease resolution, KDM5 demethylases control hepatocyte-NPC crosstalk that suppresses pro-resolving macrophages and contributes to poor fibrosis resolution.

Our data suggest that these diverse functions of KDM5 demethylases are mediated by set of transcription factors that control KDM5 expression or/and activity (chromatin binding) in hepatocytes. Some of these factors, such as C/EBPβ, STAT5B and Androgen receptor (AR) are sex-specific and are involved in sex-specific alcohol response, while others such as LXR are sex-independent.

We plan to determine the role of KDM5 demethylases in the alcohol response and identify the primary targets in males and females. The project will set the stage for further studies to understand the role of cellular communication in liver disease progression and explore the potential targets for ALD therapy.

ACLF

Acute-on-chronic liver failure (ACLF) is a clinical syndrome in which there is rapid development of liver and multi-organ system failure in a patient with previously stable cirrhosis.

Recently we identified that the key mechanism responsible for loss of liver function is linked to endothelial cell dysregulation and HGF-C/EBPβ signaling in hepatocytes. C/EBPβ is a transcription factor that regulates the expression of genes involved in the acute phase response, metabolic functions, and cell cycle progression.  C/EBPβ is transiently activated during liver regeneration. However, sustained activation is harmful because it may prevent re-differentiation. C/EBPβ is activated in ACLF mice and in human ACLF samples. Activated C/EBPβ promoted sustained suppression of metabolic and hepatocyte differentiation genes. We plan to study C/EBPβ-mediated loss of liver function in ACLF using mouse models and human liver transplant explants; and find the link between endothelial dysfunction and C/EBPβ activation.

The results of this project will define if C/EBPβ promotes liver failure in ACLF and will set the stage for future studies defining C/EBPβ function and ultimately identifying new therapeutic targets of sepsis associated ACLF.

Arginine methylation in ALD

We aimed to study the role of protein arginine methyltransferase 6 (PRMT6), a new regulator of liver function, in ALD progression.

PRMT6 expression in the liver is downregulated in ALD, and negatively correlates with disease severity in mice and human liver specimens. Prmt6-deficient mice spontaneously developed liver fibrosis after one year. In the presence of alcohol Prmt6 deficiency resulted in a dramatic increase in fibrosis development but did not affect lipid accumulation or liver injury.

Mechanistically, PRMT6 decreases pro-fibrotic signaling in liver macrophages via methylation of integrin α-4 at R464 residue. Integrin α-4 is predominantly expressed in infiltrating monocyte derived macrophages. Blocking monocyte infiltration into the liver with CCR2 inhibitor reduced fibrosis development in knockout mice and abolished differences between genotypes.

Taken together, alcohol mediated loss of Prmt6 contributes to alcohol-associated fibrosis development through reduced integrin methylation and increased pro-fibrotic signaling in macrophages.