Molecular mechanisms in MASLD/MASH-related HCC

Abstract

Liver cancer is the third leading cause of cancer-related deaths and ranks as the sixth most prevalent cancer type globally. NAFLD or metabolic dysfunction-associated steatotic liver disease, and its more severe manifestation, NASH or metabolic dysfunction-associated steatohepatitis (MASH), pose a significant global health concern, affecting approximately 20%-25% of the population. The increased prevalence of metabolic dysfunction-associated steatotic liver disease and MASH is parallel to the increasing rates of obesity-associated metabolic diseases, including type 2 diabetes, insulin resistance, and fatty liver diseases. MASH can progress to MASH-related HCC (MASH-HCC) in about 2% of cases each year, influenced by various factors such as genetic mutations, carcinogen exposure, immune microenvironment, and microbiome. MASH-HCC exhibits distinct molecular and immune characteristics compared to other causes of HCC and affects both men and women equally. The management of early to intermediate-stage MASH-HCC typically involves surgery and locoregional therapies, while advanced HCC is treated with systemic therapies, including anti-angiogenic therapies and immune checkpoint inhibitors. In this comprehensive review, we consolidate previous research findings while also providing the most current insights into the intricate molecular processes underlying MASH-HCC development. We delve into MASH-HCC-associated genetic variations and somatic mutations, disease progression and research models, multiomics analysis, immunological and microenvironmental impacts, and discuss targeted/combined therapies to overcome immune evasion and the biomarkers to recognize treatment responders. By furthering our comprehension of the molecular mechanisms underlying MASH-HCC, our goal is to catalyze the advancement of more potent treatment strategies, ultimately leading to enhanced patient outcomes.

Figure 1:. Overview of Molecular Processes in MASH-HCC Development

A. In the pre-tumorigenesis stage, lipotoxicity, oxidative stress, ER stress, and autophagy protein P62 are implicated in genome DNA damage. B. Impaired DNA repair, TAZ pathway activation, STAT3 signaling, and NOTCH pathway activation promote DNA mutations in the genome DNA, initiating HCC in MASH-hepatocytes. C. In the post-tumorigenesis phase, the TAZ pathway, ACC, cholesterol/mTORC1, GDF-15, STARD1, and ferroptosis accelerate HCC development following the tumor initiation.

Figure 2.. Immune cells involved in the pathogenesis of MASH-HCC.

Macrophage infiltration occurs in the early stage of MASH. Lipid overload and proinflammatory cytokines facilitate the formation of lipid-associated macrophages (LAMs), representing a significant shift in intrahepatic macrophage composition. LAMs play a vital role in controlling metabolic homeostasis and fibrosis. Tumor-associated macrophages (TAMs) are abundant in the tumor microenvironment. Macrophage polarization from M1 to M2 phenotype contributes essentially to the development of MASH-HCC. Dendritic cells (DCs) are heterogeneous. XCR1⁺ type 1 conventional dendritic cells (cDC1s) promote, while CD103⁺ cDC1s inhibit MASH development and potentially HCC formation. In the early MASH stage, neutrophil infiltration and neutrophil extracellular traps (NETs) formation promote the development of HCC. NETs are positively correlated with CD4⁺Foxp3⁺ Treg cells and promote Treg cell differentiation. Dysregulated lipid metabolism causes intrahepatic CD4⁺ T cell death. Liver Th17 cell subsets accelerate the transition from MASH to HCC. CD8⁺ T cells become activated in response to type 1 IFNs and intestinal-derived microbial factors, promoting MASH progression. The CXCR6⁺CD8⁺ T cells are exhausted T cells that aggravate MASH and contribute to the onset of HCC. These cells cause auto-aggressive killing and liver damage through an MHC-I independent manner. B cells are activated and infiltrate MASH livers, colocalized with T cells, promoting MASH progression by secreting proinflammatory cytokines, antibodies, and regulating T cells and macrophages' function.

Figure 3.. Immune cells crosstalk during MASH and HCC pathogenesis.

The hepatic milieu hosts a variety of immunoreactive cells in the context of MASH, operating within a complex network characterized by inflammatory and fibrogenic signaling. These cells interact mutually or engage in bidirectional communication with steatotic hepatocytes, thereby facilitating MASH progression and HCC development. In response to lipotoxic insults, steatotic and stressed hepatocytes release cytokines, chemokines, and danger-associated molecular patterns, including CCL2, CXCL10, osteopontin (OPN), extracellular vesicles, and HMGB1. These elements subsequently activate macrophages, HSCs, LSECs, and neutrophils. Macrophages play a role in shaping inflammatory, fibrotic, and anti-fibrotic processes in MASH livers. The proinflammatory milieu facilitates the recruitment of monocytes, giving rise to a heterogeneous array of monocyte-derived macrophage subsets, including TREM2⁺CD63⁺CD9⁺GPMNB⁺ lipid-associated macrophages (LAM). TNF-α/Miz and CD47/SIRPα signaling pathways facilitate intercellular communication between hepatocytes and macrophages. Steatotic hepatocytes upregulate the expression of NKG2D ligands and activate resident innate-like T cells (ILTs), which, in turn, secrete IL-17A and further promote the production of proinflammatory chemokines by hepatocytes, accelerating liver fibrosis. Neutrophils promote HSC proliferation and fibrosis accumulation. Neutrophil extracellular traps (NETs) also link innate and adaptive immune responses by facilitating Treg differentiation through the metabolic modification of naive CD4⁺ T lymphocytes. Conversely, the interaction between neutrophils and hepatocytes through neutrophil-specific miR-223 inhibits the expression of liver inflammatory and fibrogenic genes. LSECs are often recognized as the gatekeepers of hepatic immunity. LSEC capillarization, the reduction of endothelial nitric oxide (NO) bioavailability, and the upregulation of surface adhesion molecules ICAM-1 and VCAM-1 are key elements in angiogenesis, inflammation, fibrosis, and tumorigenesis. NK cells exhibit antifibrotic functions by killing HSCs and regulating macrophage M1/M2 polarization. HSC NTRK3–NTF3 autocrine signalling is also a driver of MASH fibrosis and potential contributes to MASH-HCC. These intercellular interactions promote MASH progression and, in the long term, increase the risk of HCC development. Monocyte-derived macrophages recruited to the tumor constitute the bulk of the intra-tumoral macrophage population, developing into tumor-associated macrophages (TAMs) with a heterogeneous phenotype. MASH-HCC is associated with a progressive accumulation of exhausted CD8⁺PD1⁺ T cells, lacking effective immune surveillance but mediating liver damage. CXCR6⁺CD8⁺ T cells elicit auto-aggressive cell killing independent of MHC-class I. Senescent HSCs activate ST2⁺ Treg cells and accelerate tumorigenesis through the release of IL-33. The interaction between Treg cells and neutrophil extracellular traps (NETs) contributes to the development of MASH-HCC. Blocking CCR2 expressed on tumor-associated neutrophils (TANs) increases cytotoxic anti-tumoral CD8+ T cells and reverses anti-PD-1 resistance in MASH-HCC. Natural killer T (NKT) cells accelerate the progression from MASH to HCC through the secretion of LIGHT. MASH-HCC cells suppress the anti-tumor immune response of CD8+T cells through METTL3-mediated secretion of cholesterol. MASH-HCC cells activate myeloid-derived suppressor cells (MDSCs) via the YTHDF1-EZH2-IL6 axis, contributing to the dysfunction of CD8+T cells.