CTCF regulates lipid metabolism and gene expression in mouse AML12 liver cell line

Objective·To clarify the regulatory role of CCCTC-binding factor (CTCF) in lipid metabolism in liver cells, and explore the mechanisms by which CTCF regulates liver cell gene expression.Methods·Immortalized AML12 liver cell line was used as a model to investigate the functions of CTCF in liver cells. To stably knock down Ctcf, DNA sequences stably expressing Ctcf shRNA were integrated into AML12 cells through lentivirus. The knockdown efficiency of Ctcf was verified by RT-qPCR and Western blotting. The effects of Ctcf knockdown on cell growth and cell cycle were assessed by performing CCK-8 assay and propidium iodide (PI) staining. Intracellular lipids, labeled with Oil Red O staining, were analyzed and quantified to detect the effect of CTCF on lipid metabolism and lipid droplet accumulation in AML12 cells. Changes in CTCF genome distribution after Ctcf knockdown were analyzed using the Cleavage Under Targets and Tagmentation (CUT&Tag) method. Transcriptome changes in AML12 cells after Ctcf knockdown were quantified by RNA sequencing (RNA-seq). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses, and gene set enrichment analysis (GSEA) were employed to evaluate the functions of differentially expressed genes. The correlation between gene expression changes and CTCF binding changes was further assessed by performing statistical analyses.Results·The result of RT-qPCR showed that Ctcf is downregulated 63.4% in mRNA level and 57.7% in protein level (both P<0.05). Assay of the growth curve and cycle phase confirmed that cell proliferation was inhibited in the G1/G0 phase after Ctcf knockdown. After Ctcf knockdown, AML12 cells exhibited spontaneous accumulation of intracellular lipids, indicating dysregulation of lipid metabolism (P<0.05). Genome-wide CTCF binding analysis revealed significant changes, with most differential CTCF peaks showing decreased binding, although a subset of regions exhibited increased CTCF binding. Transcriptome analyses revealed that knocking down Ctcf resulted in significant expression changes in 1 344 genes. These differentially expressed genes were enriched in lipid metabolism pathways. Further analysis showed that genes associated with regions of increased CTCF binding were enriched in pathways related to lipid transport and localization, whereas genes associated with regions of decreased CTCF binding were mainly enriched in processes such as DNA damage repair, apoptosis, and cell cycle regulation. However, the binding changes of CTCF in the genome were not sufficient to lead to the expression changes of their neighboring genes.Conclusion·CTCF affects the metabolic function of liver cells by regulating the expression of lipid metabolism-related genes. However, the binding changes of CTCF in the genome lack significant correlation with the expression of their neighboring genes, suggesting that CTCF mainly influences liver gene expression through long-distance regulation, possibly by modulating higher-order chromatin structure and enhancer-promoter interactions.