Human hepatocellular carcinoma (HCC) heterogeneity promotes recurrence and therapeutic resistance. We recently demonstrated that inflammation favors hepatocyte retrodifferentiation into progenitor cells. Here, we identify the molecular effectors that induce metabolic reprogramming, chemoresistance, and invasiveness of retrodifferentiated HCC stem cells. Spheroid cultures of human HepaRG progenitors (HepaRG-Spheres), HBG-BC2, HepG2, and HuH7 cells and isolation of side population (SP) from HepaRG cells (HepaRG-SP) were analyzed by transcriptomics, signaling pathway analysis, and evaluation of chemotherapies. Gene expression profiling of HepaRG-SP and HepaRG-Spheres revealed enriched signatures related to cancer stem cells, metastasis, and recurrence and showed that HepaRG progenitors could retrodifferentiate into an immature state. The transcriptome from these stem cells matched that of proliferative bad outcome HCCs in a cohort of 457 patients. These HCC stem cells expressed high levels of cytokines triggering retrodifferentiation and displayed high migration and invasion potential. They also showed changes in mitochondrial activity with reduced membrane potential, low ATP production, and high lactate production. These changes were, in part, related to angiopoietin-like 4 (ANGPTL4)–induced upregulation of pyruvate dehydrogenase kinase 4 (PDK4), an inhibitor of mitochondrial pyruvate dehydrogenase. Upregulation of ANGPTL4 and PDK4 paralleled that of stem cells markers in human HCC specimens. Moreover, the PDK4 inhibitor dichloroacetate reversed chemoresistance to sorafenib or cisplatin in HCC stem cells derived from four HCC cell lines. In conclusion, retrodifferentiated cancer cells develop enhanced invasion and therapeutic resistance through ANGPTL4 and PDK4. Therefore, restoration of mitochondrial activity in combination with chemotherapy represents an attractive therapeutic approach in HCC. Significance: Restoring mitochondrial function in human hepatocellular carcinomas overcomes cancer resistance.

Tumor cells display important plasticity potential, which contributes to intratumoral heterogeneity. Notably, tumor cells have the ability to retrodifferentiate toward immature states under the influence of their microenvironment. Importantly, this phenotypical conversion is paralleled by a metabolic rewiring, and according to the metabostemness theory, metabolic reprogramming represents the first step of epithelial-to-mesenchymal transition (EMT) and acquisition of stemness features. Most cancer stem cells (CSC) adopt a glycolytic phenotype even though cells retain functional mitochondria. Such adaptation is suggested to reduce the production of reactive oxygen species (ROS), protecting CSC from detrimental effects of ROS. CSC may also rely on glutaminolysis or fatty acid metabolism to sustain their energy needs. Besides pro-inflammatory cytokines that are well-known to initiate the retrodifferentiation process, the release of catecholamines in the microenvironment of the tumor can modulate both EMT and metabolic changes in cancer cells through the activation of EMT transcription factors (ZEB1, Snail, or Slug (SNAI2)). Importantly, the acquisition of stem cell properties favors the resistance to standard care chemotherapies. Hence, a better understanding of this process could pave the way for the development of therapies targeting CSC metabolism, providing new strategies to eradicate the whole tumor mass in cancers with unmet needs.

Steatosis is a liver lesion reported with numerous pharmaceuticals. Prior studies showed that severe impairment of mitochondrial fatty acid oxidation (mtFAO) constantly leads to lipid accretion in liver. However, much less is known about the mechanism(s) of drug-induced steatosis in the absence of severe mitochondrial dysfunction, although previous studies suggested the involvement of mild-to-moderate inhibition of mtFAO, increased de novo lipogenesis (DNL), and impairment of very low-density lipoprotein (VLDL) secretion. The objective of our study, mainly carried out in human hepatoma HepaRG cells, was to investigate these 3 mechanisms with 12 drugs able to induce steatosis in human: amiodarone (AMIO, used as positive control), allopurinol (ALLO),d-penicillamine (DPEN), 5-fluorouracil (5FU), indinavir (INDI), indomethacin (INDO), methimazole (METHI), methotrexate (METHO), nifedipine (NIF), rifampicin (RIF), sulindac (SUL), and troglitazone (TRO). Hepatic cells were exposed to drugs for 4 days with concentrations decreasing ATP level by less than 30% as compared to control and not exceeding 100 × C_max. Among the 12 drugs, AMIO, ALLO, 5FU, INDI, INDO, METHO, RIF, SUL, and TRO induced steatosis in HepaRG cells. AMIO, INDO, and RIF decreased mtFAO. AMIO, INDO, and SUL enhanced DNL. ALLO, 5FU, INDI, INDO, SUL, RIF, and TRO impaired VLDL secretion. These seven drugs reduced the mRNA level of genes playing a major role in VLDL assembly and also induced endoplasmic reticulum (ER) stress. Thus, in the absence of severe mitochondrial dysfunction, drug-induced steatosis can be triggered by different mechanisms, although impairment of VLDL secretion seems more frequently involved, possibly as a consequence of ER stress.

Cigarette smoke exposure (CS) is the main risk factor for chronic obstructive pulmonary disease (COPD). Macrophages have an important role in COPD because they release pro-inflammatory and anti-inflammatory cytokines. The present study’s we investigate the functional changes in macrophages and monocytes exposed to cigarette smoke extract (CSE). Herein, using human monocyte-derived macrophages (MDMs) from healthy donors and we found that CSE was not associated with significant changes in the production of pro inflammatory cytokines by MDMs. In contrast, exposure to CSE suppressed the production of IL-6 and Gro-a/CXCL1 by LPS-stimulated-MDMs, but had an additive effect on the release of IL-8/CXCL8 and MCP1/CCL2. However, CSE exposure was associated with greater production, TARC/CCL-17 and CCL22/MDC. Moreover, MDMs displayed a lower uptake capacity after CSE exposure. We identify, for what is to our knowledge the first time that monocytes from patients with COPD produced less IL-8/CXCL8 and Gro-α/CXCL1 after LPS stimulation and produced higher levels of TARC/CCL17 and MDC/CCL-22 after IL-4 stimulation. Our present results highlighted a skewed immune response, with an imbalance in M1 vs. M2 cytokine production. In conclusion, exposure to CS has contrasting, multifaceted effects on macrophages and monocytes. Our data may provide a better understanding of the mechanisms underlying COPD.

Human hepatocellular carcinomas (HCCs) with cancer stem cell (CSC) features are a subclass of therapeutically challenging cancers. We recently showed that retrodifferentiation of hepatic cancer cells into CSC-like cells leads to metabolic reprogramming and chemoresistance. The molecular mechanisms whereby differentiated cancer cells switch towards a CSC phenotype are poorly understood. By studying metabolic reprogramming associated with HCC cell plasticity, we identified an unsuspected role of peroxisome proliferator-activated receptor (PPAR)γ in hepatic CSC phenotype acquisition. Gene expression and metabolic analyses performed throughout the cell differentiation/retrodifferentiation process of human HepaRG and HBG-BC2 HCC cells show that metabolic reprogramming in hepatic CSCs is associated with a fragmented mitochondrial network, decreased respiration, de novo lipogenesis, and fatty acid oxidation, but increased glycolysis and lipid storage. Mitochondrial genes downregulated in HepaRG-CSCs are also downregulated in the STEM HCC subclass. While PPARα is the main isoform in differentiated hepatic cells, we find high PPARγ expression in hepatic CSCs. Accordingly, nuclear localization of PPARγ is detected in human HCC tumors, and PPARγ ^high /PPARα ^low expression is associated with the STEM HCC subclass and a poor outcome in human HCC cohorts. PPARγ silencing or/and inhibition of its target gene pyruvate dehydrogenase kinase 4 reactivates cell respiration, increases reactive oxygen species production and sensitizes hepatic CSCs to chemotherapy. Conversely, PPARα activation synergizes with chemotherapy to induce cell death. Targeting PPARγ, a key regulator of metabolic reprogramming and stemness in hepatic CSCs, or modulating the PPARγ/PPARα balance that finely tunes the differentiation/retrodifferentiation process in HCC deserves further investigation for anti-tumor therapy.

La plasticité des hépatocytes tumoraux leur permet de se rétrodifférencier en cellules souches cancéreuses (CSC) sous l’influence de signaux pro-inflammatoires. Cette rétrodifférenciation contribue à l’hétérogénéité des carcinomes hépatocellulaires (CHC) et à leur chimiorésistance. Il a été démontré récemment que les processus de différenciation/rétrodifférenciation s’accompagnent d’une reprogrammation métabolique. Notre projet vise à caractériser la reprogrammation métabolique des hépatocytes tumoraux en fonction de leur état de différenciation et à identifier des acteurs du métabolisme cellulaire susceptibles de constituer de nouvelles cibles thérapeutiques. Pour modéliser la diversité des CHC, nous utilisons des lignées cellulaires qui présentent des aptitudes de différenciation/ rétrodifférenciation différentes. Nos résultats montrent que les cellules hépatiques les plus immatures présentent un réseau mitochondrial moins développé, une diminution de l’activité mitochondriale se traduisant par une phosphorylation oxydative, une glutaminolyse, une β-oxydation, une lipogenèse de novo et une élongation des acides gras diminuées. En corollaire, la glycolyse basale et la production de lactate sont augmentées. Nous avons également mis en évidence que les CSC hépatiques captent des quantités importantes d’acides gras dans leur environnement et qu’elles les stockent sous forme de gouttelettes lipidiques. Ces modifications du métabolisme lipidique en fonction de l’état de différenciation cellulaire nous a amenés à étudier la famille de récepteurs nucléaires PPAR, connue pour son rôle dans la différenciation et l’homéostasie métabolique. Nous montrons que PPARγ favorise la rétrodifférenciation des hépatocytes tumoraux qui se traduit par une augmentation des marqueurs d’EMT et de cellules souches. Cette rétrodifférenciation s’accompagne également d’une diminution du nombre de branchements et de la longueur du réseau mitochondrial ainsi qu’une faible respiration mitochondriale. L’analyse de cohortes de CHC montre que PPARγ est associé à un mauvais pronostic tandis que PPARα, qui augmente au cours de la différenciation cellulaire, est lui un facteur de bon pronostic. L’inhibition de PPARγ augmente la longueur et le nombre de branchements du réseau mitochondrial et réactive l’OXPHOS ce qui génère une production de ROS, provoquant la mort des CSC hépatiques. L’activation de PPARα provoque également une augmentation de la longueur du réseau mitochondrial et induit, en association avec le DCA, une mortalité cellulaire dans les CSC. Il apparaît donc intéressant d’évaluer les thérapies ciblant PPARα ou PPARγ en complément des chimiothérapies pour limiter la récurrence des CHC.