Mitochondrial alterations and signatures in hepatocellular carcinoma

Abstract

Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer worldwide. Its primary risk factors are chronic liver diseases such as metabolic fatty liver disease, non-alcoholic steatohepatitis, and hepatitis B and C viral infections. These conditions contribute to a specific microenvironment in liver tumors which affects mitochondrial function. Mitochondria are energy producers in cells and are responsible for maintaining normal functions by controlling mitochondrial redox homeostasis, metabolism, bioenergetics, and cell death pathways. HCC involves abnormal mitochondrial functions, such as accumulation of reactive oxygen species, oxidative stress, hypoxia, impairment of the mitochondrial unfolded protein response, irregularities in mitochondrial dynamic fusion/fission mechanisms, and mitophagy. Cell death mechanisms, such as necroptosis, pyroptosis, ferroptosis, and cuproptosis, contribute to hepatocarcinogenesis and play a significant role in chemoresistance. The relationship between mitochondrial dynamics and HCC is thus noteworthy. In this review, we summarize the recent advances in mitochondrial alterations and signatures in HCC and attempt to elucidate its molecular biology. Here, we provide an overview of the mitochondrial processes involved in hepatocarcinogenesis and offer new insights into the molecular pathology of the disease. This may help guide future research focused on improving patient outcomes using innovative therapies.

Keywords: Chemoresistance; Hepatocarcinogenesis; Hepatocellular carcinoma; Mitochondria; Mitochondrial dynamics.

Fig. 1

Mitochondrial pathways in Hepatocellular Carcinoma (HCC) pathogenesis. During HCC development, increased mitochondrial activity leads to increased reactive oxygen species (ROS) levels. This induces antioxidant systems such as NAD⁺-dependent deacetylase sirtuin-3 (SIRT3) and superoxide dismutase 2 (SOD2), to neutralize reactive oxygen species (ROS). However, continuous ROS accumulation lowers mitochondrial efficiency, activates AMP-activated protein kinase (AMPK) and proliferator-activated receptor γ coactivators 1-α (PGC-1α) transcription mechanisms, and triggers the expression of mitochondrial adaptive gene pathways. Abnormalities in mitochondrial unfolded protein response (mtUPR) can also promote the occurrence and hepatocarcinogenesis of HCC. Normally, damaged mitochondria are cleared via mitophagy; however, lipid accumulation hinders this process. If mitophagy is blocked, the damaged mitochondria split and release inflammatory damage associated mitochondrial molecular patterns (DAMPs) and cytochrome C, thus driving hepatocarcinogenesis. Temporal alterations in lipid metabolism, one-carbon metabolism, and amino acid biosynthesis trigger compensatory proliferation of cancer cells, further intensifying hypoxia, DNA damage, mutations, and evasion of cell cycle checkpoints. The X proteins include Forkhead Box O3 (FoxO3), Isocitrate Dehydrogenase (NADP⁺) 2 (IDH2), Pyruvate Dehydrogenase (PDH), NADH:Ubiquinone Oxidoreductase Subunit A9 (NDUFA9, Complex I), and Succinate Dehydrogenase Complex Flavoprotein Subunit A (SDHA, Complex II). Ac, acetylated; ATP, adenosine triphosphate; BNIP3, BCL2 interacting protein 3; ER, endoplasmic reticulum; ERR, estrogen-related receptor; HCC, hepatocellular carcinoma; HMGB1, high mobility group box 1; JNK, c-Jun N-terminal kinase; LC3, microtubule-associated protein 1A/1B-light chain 3; IL1α, interleukin 1α; mtDNA, mitochondrial DNA; NIX, NIP3-like protein X; NRF1/2, nuclear respiratory factor 1/2; P62, p62/SQSTM1; PAMPs, pathogen-associated molecular patterns; PINK1, PTEN-induced kinase 1; PPAK, peroxisome proliferator-activated receptor; Ub, ubiquitin. "↑" represents an increase, while "↓" represents a decrease. The arrow symbolizes promotion, while the blunt line represents inhibition

Fig. 2

Mitochondrial dynamics during cell cycle progression. During the G0 phase, mitochondria undergo fusion, fission, and depolarization. Mitochondrial fusion proteins 1 and 2 (MFN1/2) and optic atrophy 1 (OPA1) facilitate mitochondrial fusion. Mitochondrial fission relies on dynamin-related protein 1 (DRP1) and mitochondrial fission factor (MFF). Eventually, fragmented and dysfunctional mitochondria are discarded via mitophagy. The mitophagy receptors BCL2 interacting protein 3 (BNIP3) and NIP3-like protein X (NIX) bind to microtubule-associated protein 1A/1B-light chain 3 (LC3), associating mitochondria with autophagosomes. PTEN-induced kinase 1 (PINK1) accumulates on the surface of depolarized mitochondria and phosphorylates ubiquitinated mitochondrial outer membrane proteins, including parkin, which further promotes ubiquitination of these proteins. The p62/SQSTM1 link recognizes ubiquitinated proteins and triggers mitophagy. In different phases of the cell cycle, mitochondria undergo hyperfusion during the G1-S phase, fragmentation during the S phase, and dispersion during the M phase. FIS, mitochondrial fission protein; OXPHOS, oxidative phosphorylation; ROS, reactive oxygen species; Ub, ubiquitin. "↑" represents an increase, while "↓" represents a decrease. The arrow symbolizes promotion

Fig. 3

Molecular mechanisms of necroptosis/pyroptosis in HCC. Binding of tumor necrosis factor (TNF) to its receptor initiates both necroptosis and apoptosis. In collaboration with receptor-interacting protein kinase 1 (RIPK1), Fas-associated death domain (FADD), and TNFR1-associated death domain protein (TRADD)/ receptor-interacting protein kinase 3 (RIPK3), caspase 8 triggers apoptosis. However, if Casp 8 inhibition promotes mixed lineage kinase domain-like pseudokinase (MLKL), RIPK1, and RIPK3 expression, leading to necrosome formation. Viral infections and mitochondrial damage can activate the Z-DNA Binding Protein 1 (ZBP1)-RIPK3 pathway, resulting in necrosome formation. Once phosphorylated, MLKL creates membrane pores which facilitate the release of specific damage-associated molecular pattern (DAMPs) molecules. Simultaneously, the accumulation of extracellular sodium ion (Na⁺) and calcium ion (Ca²⁺) in the cytoplasm leads to cell swelling and cell membrane rupture. DAMPs trigger pyroptosis through pattern recognition receptor (PRR). The NOD-like receptor family pyrin domain containing 3 (NLRP3) receptors, along with NIMA-related kinase 7 (NEK7), apoptosis associated dot like protein (ASC), and Pro-casp 1, forms the NLRP3 inflammasome. The inflammasome then triggers Casp-1, which promotes Gasdermin D (GSDMD) cleavage. Casp-4/5 activation leads to GSDMD cleavage. The N-terminal fragment of GSDMD forms a membrane pore, leading to the release of cytoplasmic contents, electrolytes, and specific cytokines such as interleukin (IL) 1α, IL-1β, IL-18, and leukotriene B4 (LTB4). Concurrently, potassium ion (K⁺) in the cytoplasm is expelled from the cells. ATP, adenosine triphosphate; C, C terminal; Casp4/5, caspase 4/5; Casp8, caspase 8; cIAP1/2, cellular inhibitor of apoptosis protein 1/2; HMGB1, high mobility group box 1; LPS, lipopolysaccharide; mtDNA, mitochondrial DNA; N, N terminal; P, phosphate group; PAMPs, pathogen-associated molecular pattern; ROS, reactive oxygen species; TNFR, tumor necrosis factor receptor; TRAF2, TNF receptor-associated factor 2; TRAF5, TNF receptor-associated factor 5. The arrow symbolizes promotion, while the blunt line represents inhibition. Black arrows indicate the entry and exit directions across the cell membrane

Fig. 4

Molecular mechanisms of ferroptosis/cuproptosis in HCC. An influx of cysteine into tumor cells can lead to accumulation of the cysteine-glutathione (GSH)-glutathione peroxidase 4 (GP_X4) axis. Ferroptosis is triggered by the synthesis and peroxidation of polyunsaturated fatty acid-containing phospholipids (PUFA-PLs), iron metabolism, and mitochondrial metabolism. The defense system against ferroptosis mainly comprises the GSH, ferroptosis suppressor protein-1 (FSP1)-ubiquinol (reduced form of coenzyme Q₁₀, CoQ₁₀H₂), dihydroorotate dehydrogenase (DHODH)-CoQ₁₀H₂, and GTP cyclohydrolase-1 (GCH1)-tetrahydrobiopterin (BH4) systems. A decrease in intracellular GSH levels or GP_X4 activity can lead to the excessive accumulation of intracellular lipid reactive oxygen species (ROS) and lipid peroxidation. Iron initiates a non-enzymatic Fenton reaction and serves as a cofactor for arachidonic acid lipoxygenase (ALOX) and cytochrome P450 oxidoreductase (POR). It promotes lipid peroxidation and mitochondrial metabolism and enhances ROS, adenosine triphosphate (ATP), and PUFA-PL. FSP1 prevents iron-induced apoptosis through NAD(P)-H-catalyzed Co-enzyme Q10 (CoQ10) regeneration. FIN56 induces iron toxicity by enhancing GP_X4 degradation and reducing CoQ10 levels. If ferroptosis promotion substantially exceed the detoxification capacity of the ferroptotic defense system, lethal accumulation of lipid peroxides on the cell membrane can cause membrane rupture and ferroptotic cell death. Oxidative damage to mitochondrial membranes impairs enzyme function in the tricarboxylic acid (TCA) cycle, leading to carboxy proptosis. The key factors in Cu-ionophore-induced cell death are Ferredoxin 1 (FDX1) and protein-lipid sequestration. Excessive Cu can cause aggregation and loss of function of lipid-sequestering proteins, resulting in the instability of Fe-S cluster proteins. FDX1 reduces Copper II (Cu²⁺) to Copper I (Cu⁺), whereas GSH prevents cuproptosis. The presence of Cu⁺ promotes lipid acylation and enzyme aggregation, particularly in enzymes involved in regulating the mitochondrial TCA cycle, such as dihydrolipoamide S-Acetyltransferase (DLAT). This, along with the instability of Fe-S cluster proteins, damages the mitochondrial membrane and TCA cycle, leading to Cu-induced apoptosis. ATPase Cu transporting beta (ATP7B) also regulates Cu-ion accumulation by mediating Cu-ion entry and exocytosis. α-KG, α-ketoglutaric acid; Cys, Cysteine; Fe²⁺, ferrous iron; Gln, Glutamine; Glu, Glutamate; GSSG, Glutathione disulfide; LA, ipoylation; LAT, dihydrolipoamide S-acetyltransferase; LIAS, lipoyl synthase; PUFA, polyunsaturated fatty acid-containing; SLC3A2, solute carrier family 3 member 2; SLC31A1, solute carrier family 31 member 1; SLC7A11, solute carrier family 7 member 11; STEAP, 6-transmembrane epithelial antigen of prostate; TFRC, transferrin receptor protein 1