Hepatocellular carcinoma (HCC) is one of the most aggressive types of cancer and lacks effective therapeutic approaches. Most HCC develops in the setting of chronic liver injury, hepatic inflammation, and fibrosis. Hepatic stellate cells (HSCs) and cancer-associated fibroblasts (CAFs) are key players in liver fibrogenesis and hepatocarcinogenesis, respectively. CAFs, which probably derive from HSCs, activate into extracellular matrix (ECM)-producing myofibroblasts and crosstalk with cancer cells to affect tumor growth and invasion. In this review, we describe the different components which form the HCC premalignant microenvironment (PME) and the tumor microenvironment (TME), focusing on the liver fibrosis process and the biology of CAFs. We will describe the CAF-dependent mechanisms which have been suggested to promote hepatocarcinogenesis, such as the alteration of ECM, CAF-dependent production of cytokines and angiogenic factors, CAF-dependent reduction of immuno-surveillance, and CAF-dependent promotion of epithelial-mesenchymal transition (EMT). New knowledge of the fibrosis process and the role of CAFs in HCC may pave the way for new therapeutic strategies for liver cancer.

UNLABELLED: Hepatic fibrogenesis is a pathophysiological outcome of chronic liver injury hallmarked by excessive accumulation of extracellular matrix proteins. Fibrosis is a dynamic process that involves cross-talk between parenchymal cells (hepatocytes), hepatic stellate cells, sinusoidal endothelial cells and both resident and infiltrating immune cells. In this review, we focus on key cell-types that contribute to liver fibrosis, cytokines, and chemokines influencing this process and what it takes for fibrosis to regress. We discuss how mitochondria and metabolic changes in hepatic stellate cells modulate the fibrogenic process. We also briefly review how the presence of fibrosis affects development of hepatocellular carcinoma. IMPACT STATEMENT: Advanced liver fibrosis results in cirrhosis, portal hypertension, and liver failure and often requires liver transplantation. Advanced liver fibrosis and cirrhosis are also major risk factors for hepatocellular carcinoma (HCC). Hepatic stellate cells (HSCs) play a pivotal role in the pathogenesis of liver fibrosis. In this review, we summarize the basic mechanisms that influence liver fibrosis development and how oxidative stress, mitochondrial dysfunction, and metabolic remodeling modulate HSC activation and indicate areas of potential therapeutic intervention.

Liver fibrosis is a clinically significant finding that has major impacts on patient morbidity and mortality. The mechanism of fibrosis involves many different cellular pathways, but the major cell type involved appears to be hepatic stellate cells. Many liver diseases, including Hepatitis B, C, and fatty liver disease cause ongoing hepatocellular damage leading to liver fibrosis. No matter the cause of liver disease, liver-related mortality increases exponentially with increasing fibrosis. The progression to cirrhosis brings more dramatic mortality and higher incidence of hepatocellular carcinoma. Fibrosis can also affect outcomes following liver transplantation in adult and pediatric patients and require retransplantation. Drugs exist to treat Hepatitis B and C that reverse fibrosis in patients with those viral diseases, but there are currently no therapies to directly treat liver fibrosis. Several mouse models of chronic liver diseases have been successfully reversed using novel drug targets with current therapies focusing mostly on prevention of myofibroblast activation. Further research in these areas could lead to development of drugs to treat fibrosis, which will have invaluable impact on patient survival. This article is categorized under: Metabolic Diseases > Molecular and Cellular Physiology.

Although hepatocellular cancer (HCC) usually occurs in the setting of liver fibrosis, the causal relationship between liver fibrosis and HCC is unclear. in vivo and in vitro models of HCC involving Col^r/r mice (that produce a collagenase-resistant type I collagen) or wild-type (WT) mice were used to assess the relationship between type I collagen, liver fibrosis, and experimental HCC. HCC was either chemically induced in WT and Col^r/r mice or Hepa 1-6 cells were engrafted into WT and Col^r/r livers. The effect of hepatic stellate cells (HSCs) from WT and Col^r/r mice on the growth of Hepa 1-6 cells was studied by using multicellular tumor spheroids and xenografts. Collagen type I deposition and fibrosis were increased in Col^r/r mice, but they developed fewer and smaller tumors. Hepa 1-6 cells had reduced tumor growth in the livers of Col^r/r mice. Although Col^r/r HSCs exhibited a more activated phenotype, Hepa 1-6 growth and malignancy were suppressed in multicellular tumor spheroids and in xenografts containing Col^r/r HSCs. Treatment with vitronectin, which mimics the presence of degraded collagen fragments, converted the Col^r/r phenotype into a WT phenotype. Although Col^r/r mice have increased liver fibrosis, they exhibited decreased HCC in several models. Thus, increased liver type I collagen does not produce increased experimental HCC.

Alcoholic liver disease (ALD) is a leading cause of cirrhosis in the United States, which is characterized by extensive deposition of extracellular matrix proteins and formation of a fibrous scar. Hepatic stellate cells (HSCs) are the major source of collagen type 1 producing myofibroblasts in ALD fibrosis. However, the mechanism of alcohol-induced activation of human and mouse HSCs is not fully understood. We compared the gene-expression profiles of primary cultured human HSCs (hHSCs) isolated from patients with ALD (n = 3) or without underlying liver disease (n = 4) using RNA-sequencing analysis. Furthermore, the gene-expression profile of ALD hHSCs was compared with that of alcohol-activated mHSCs (isolated from intragastric alcohol-fed mice) or CCl₄-activated mouse HSCs (mHSCs). Comparative transcriptome analysis revealed that ALD hHSCs, in addition to alcohol-activated and CCl₄-activated mHSCs, share the expression of common HSC activation (Col1a1 [collagen type I alpha 1 chain], Acta1 [actin alpha 1, skeletal muscle], PAI1 [plasminogen activator inhibitor-1], TIMP1 [tissue inhibitor of metalloproteinase 1], and LOXL2 [lysyl oxidase homolog 2]), indicating that a common mechanism underlies the activation of human and mouse HSCs. Furthermore, alcohol-activated mHSCs most closely recapitulate the gene-expression profile of ALD hHSCs. We identified the genes that are similarly and uniquely up-regulated in primary cultured alcohol-activated hHSCs and freshly isolated mHSCs, which include CSF1R (macrophage colony-stimulating factor 1 receptor), PLEK (pleckstrin), LAPTM5 (lysosmal-associated transmembrane protein 5), CD74 (class I transactivator, the invariant chain), CD53, MMP9 (matrix metallopeptidase 9), CD14, CTSS (cathepsin S), TYROBP (TYRO protein tyrosine kinase-binding protein), and ITGB2 (integrin beta-2), and other genes (compared with CCl₄-activated mHSCs). Conclusion: We identified genes in alcohol-activated mHSCs from intragastric alcohol-fed mice that are largely consistent with the gene-expression profile of primary cultured hHSCs from patients with ALD. These genes are unique to alcohol-induced HSC activation in two species, and therefore may become targets or readout for antifibrotic therapy in experimental models of ALD.

We investigated the role of mesothelin (Msln) and thymocyte differentiation antigen 1 (Thy1) in the activation of fibroblasts across multiple organs and demonstrated that Msln^-/- mice are protected from cholestatic fibrosis caused by Mdr2 (multidrug resistance gene 2) deficiency, bleomycin-induced lung fibrosis, and UUO (unilateral urinary obstruction)-induced kidney fibrosis. On the contrary, Thy1^-/- mice are more susceptible to fibrosis, suggesting that a Msln-Thy1 signaling complex is critical for tissue fibroblast activation. A similar mechanism was observed in human activated portal fibroblasts (aPFs). Targeting of human MSLN⁺ aPFs with two anti-MSLN immunotoxins killed fibroblasts engineered to express human mesothelin and reduced collagen deposition in livers of bile duct ligation (BDL)-injured mice. We provide evidence that antimesothelin-based therapy may be a strategy for treatment of parenchymal organ fibrosis.

Chronic alcohol abuse has a detrimental effect on the brain and liver. There is no effective treatment for these patients, and the mechanism underlying alcohol addiction and consequent alcohol-induced damage of the liver/brain axis remains unresolved. We compared experimental models of alcoholic liver disease (ALD) and alcohol dependence in mice and demonstrated that genetic ablation of IL-17 receptor A (IL-17ra-/-) or pharmacological blockade of IL-17 signaling effectively suppressed the increased voluntary alcohol drinking in alcohol-dependent mice and blocked alcohol-induced hepatocellular and neurological damage. The level of circulating IL-17A positively correlated with the alcohol use in excessive drinkers and was further increased in patients with ALD as compared with healthy individuals. Our data suggest that IL-17A is a common mediator of excessive alcohol consumption and alcohol-induced liver/brain injury, and targeting IL-17A may provide a novel strategy for treatment of alcohol-induced pathology.