Background and Aims: HSCs contribute to HCC progression by regulating multiple factors. However, the entire immunoregulatory functions of HSCs are still obscure. Here, we aim to investigate whether HSCs impose CX₃CR1⁺ macrophages to protumorigenic properties in the peritumoral area. Approach and Results: In single-cell RNA-sequencing analysis of patients with HCC, a subpopulation of macrophages specifically expressed Arg1 and Cx3cr1 in the peritumoral area and were highly enriched with retinol metabolism–related genes. Flow cytometry analysis showed significantly increased frequencies of CD14⁺CD11b⁺HLA-DR⁻ macrophages with CX₃CR1 in the HCC adjacent region where α-smooth muscle actin–expressing activated hepatic stellate cells (aHSCs) showed colocalized expression of CX₃CL1. Accordingly, in tumor-bearing mice, Cx3cl1 mRNA expression was notably increased in aHSCs within the adjacent HCC, where infiltration of CX₃CR1⁺Ly6C⁺ macrophages was mostly observed with decreased CD8⁺ T cells. In adoptive transfer and in vitro coculture of myeloid cells, we demonstrated that CX₃CR1⁺Ly6C⁺ macrophages migrated and highly expressed arginase-1 by interacting with retinoid-enriched aHSCs in the adjacent HCC. Direct treatment of retinoids or coculturing with retinol-storing mouse aHSCs or human LX-2 cells significantly increased arginase-1 expression in CX₃CR1⁺Ly6C⁺ macrophages and human blood CD14⁺ cells, leading to the suppression of CD8⁺ T-cell proliferation. Moreover, genetic deficiency of CX₃CR1 in myeloid cells or pharmacological inhibition of retinol metabolism remarkably attenuated HCC development. Conclusions: We showed that CX₃CR1⁺Ly6C⁺ macrophages migrate and interact with aHSCs in the peritumoral region where retinoids induce arginase-1 expression in CX₃CR1⁺Ly6C⁺ macrophages, subsequently depriving CD8⁺ T cells of arginine and promoting HCC.

Alcohol-related liver disease (ALD) became an important health issue worldwide. Following chronic alcohol consumption, the development of ALD might be caused by metabolic and immunologic factors, such as reactive oxygen species (ROS) and pro-inflammatory cytokines. For example, hepatic cytochrome P450 2E1 enzyme increases ROS production and stimulates de novo lipogenesis after alcohol exposure. In addition, damage- and pathogen-associated molecular patterns stimulate their specific receptors in non-parenchymal cells, including Kupffer cells, hepatic stellate cells (HSCs), and lymphocytes, which result in hepatocyte death and infiltration of pro-inflammatory cells (e.g., neutrophils and macrophages) in the liver. Moreover, our studies have suggested the novel involvement of neurologic signaling pathways (e.g., endocannabinoid and glutamate) through the metabolic synapse between hepatocytes and HSCs in the development of alcohol-related hepatic steatosis. Additionally, agouti-related protein and beta2-adrenergic receptors aggravate hepatic steatosis. Furthermore, organ-crosstalk has emerged as a critical issue in ALD. Chronic alcohol consumption induces dysbiosis and barrier disruption in the gut, leading to endotoxin leakage into the portal circulation, or lipolysis-mediated transport of triglycerides from the adipose tissue to the liver. In summary, this review addresses multiple pathogeneses of ALD, provides novel neurologic signaling pathways, and emphasizes the importance of organ-crosstalk in the development of ALD.

Glutamate, a crucial player in hepatic amino acid metabolism, has been relatively unexplored in immune cell activation. We show in a study with male mice that hepatic glutamate accumulates in vesicles of perivenous hepatocytes through vesicular glutamate transporter 3 (VGLUT3), regulated by the aryl hydrocarbon receptor upon chronic alcohol intake. Additional binge drinking triggers the exocytosis of glutamate by altering the intracellular Ca²⁺ level, stimulating metabotropic glutamate receptor 5 (mGluR5) and subsequent NADPH oxidase 2 (NOX2)-mediated ROS production in Kupffer cells (KCs). This interaction between hepatocytes and KCs is facilitated by pseudosynapse formation, arising from alcohol-induced ballooning of perivenous hepatocytes. Genetic or pharmacological interference of mGluR5 or NOX2 in KCs alleviates alcohol-related steatohepatitis (ASH). Analysis of patient samples confirmed some of the findings from mice, showing that plasma glutamate concentration and VGLUT3 levels correlate with ASH development. Conclusively, our findings highlight glutamate storage and release in mediating ASH, particularly through the pseudosynapse between hepatocytes and KCs.

Cancer stem cells (CSCs) within the tumor bulk play crucial roles in tumor initiation, recurrence and therapeutic resistance. In addition to intrinsic regulation, a growing body of evidence suggests that the phenotypes of CSCs are also regulated extrinsically by stromal cells in the tumor microenvironment (TME). Here, we discuss the current knowledge of the interplay between stromal cells and cancer cells with a special focus on how stromal cells drive the stemness of cancer cells and immune evasive mechanisms of CSCs. Knowledge gained from the interaction between CSCs and stromal cells will provide a mechanistic basis for the development of novel therapeutic strategies for the treatment of cancers.

Increasing evidence indicates that activation of oncogenic pathways contributes to an unfavourable tumour immune microenvironment (TIME), ultimately resulting in resistance to immunotherapy. Here, we aim to identify a critical oncogenic pathway involved in an antigen-expressing c-MYC-lucOS^OE/Tp53^KO hepatocellular carcinoma (HCC) mouse model that simulates immune response against tumour-associated antigens. Using data-independent acquisition proteomics, we reveal the role of wild-type KRAS in immune escaped mouse HCC tumours, with EGF concurrently activating EGFR/MEK/ERK signalling. Single cell RNA sequencing data analysis reveals that KRAS signalling intrinsically inhibits interferon-mediated MHC-I expression and extrinsically impairs CD8⁺ T cell activity due to the suppression of CXCL9 through the EGFR/MEK/ERK pathway. We observe KRAS activation in HCC patients who received immune checkpoint inhibitor (ICI) treatments, where it correlates with poor clinical outcomes. Notably, combination therapy with SOS1 inhibitor MRTX0902, Trametinib, and anti-PD-1 antibody effectively increased intratumoural CD8⁺ T cell infiltration and improved survival. Our study thus reveals that targeting wild-type KRAS signalling in combination with ICIs may serve as an effective treatment strategy for advanced HCC patients.