Expression of Cyclin E1 in hepatic stellate cells is critical for the induction and progression of liver fibrosis and hepatocellular carcinoma in mice.

Hepatocellular carcinoma (HCC) is one of the most severe malignancies with increasing incidence and limited treatment options. Typically, HCC develops during a multistep process involving chronic liver inflammation and liver fibrosis. The latter is characterized by the accumulation of extracellular matrix produced by Hepatic Stellate Cells (HSCs). This process involves cell cycle re-entry and proliferation of normally quiescent HSCs in an ordered sequence that is highly regulated by cyclins and associated cyclin-dependent kinases (CDKs) such as the Cyclin E1 (CCNE1)/CDK2 kinase complex. In the present study, we examined the role of Cyclin E1 (Ccne1) and Cdk2 genes in HSCs for liver fibrogenesis and hepatocarcinogenesis. To this end, we generated conditional knockout mice lacking Ccne1 or Cdk2 specifically in HSCs (Ccne1∆HSC or Cdk2∆HSC). Ccne1∆HSC mice showed significantly reduced liver fibrosis formation and attenuated HSC activation in the carbon tetrachloride (CCl4) model. In a combined model of fibrosis-driven hepatocarcinogenesis, Ccne1∆HSC mice revealed decreased HSC activation even after long-term observation and substantially reduced tumor load in the liver when compared to wild-type controls. Importantly, the deletion of Cdk2 in HSCs also resulted in attenuated liver fibrosis after chronic CCl4 treatment. Single-cell RNA sequencing revealed that only a small fraction of HSCs expressed Ccne1/Cdk2 at a distinct time point after CCl4 treatment. In summary, we provide evidence that Ccne1 expression in a small population of HSCs is sufficient to trigger extensive liver fibrosis and hepatocarcinogenesis in a Cdk2-dependent manner. Thus, HSC-specific targeting of Ccne1 or Cdk2 in patients with liver fibrosis and high risk for HCC development could be therapeutically beneficial.

Combined Therapy with a CCR2/CCR5 Antagonist and FGF21 Analogue Synergizes in Ameliorating Steatohepatitis and Fibrosis.

(1) Background: With new potential drug targets emerging, combination therapies appear attractive to treat non-alcoholic steatohepatitis (NASH) and fibrosis. Chemokine receptor CCR2/5 antagonists can improve fibrosis by reducing monocyte infiltration and altering hepatic macrophage subsets. Fibroblast growth factor 21 (FGF21) may improve NASH by modulating lipid and glucose metabolism. We compared effects of single drug to combination treatment as therapeutic strategies against NASH. (2) Methods: We analyzed serum samples and liver biopsies from 85 nonalcoholic fatty liver disease (NAFLD) patients. A CCR2/5 inhibitor (BMS-687681-02-020) and a pegylated FGF21 agonist (BMS-986171) were tested in male C57BL/6J mice subjected to dietary models of NASH and fibrosis (choline-deficient, L-amino acid-defined, high-fat diet (CDAHFD) up to 12 weeks; short- (2w) or long-term (6w) treatment). (3) Results: In NAFLD patients, chemokine CCL2 and FGF21 serum levels correlated with inflammatory serum markers, only CCL2 was significantly associated with advanced liver fibrosis. In rodent NASH, CCR2/5 inhibition significantly reduced circulating Ly6C+ monocytes and hepatic monocyte-derived macrophages, alongside reduced hepatic inflammation and fibrosis. FGF21 agonism decreased body weight, liver triglycerides and histological NASH activity. Combination treatment reflected aspects of both compounds upon short- and long-term application, thereby amplifying beneficial effects on all aspects of steatohepatitis and fibrosis. (4) Conclusions: CCR2/5 inhibition blocks hepatic infiltration of inflammatory monocytes, FGF21 agonism improves obesity-related metabolic disorders. Combined therapy ameliorates steatohepatitis and fibrosis more potently than single drug treatment in rodent NASH, corroborating the therapeutic potential of combining these two approaches in NASH patients.

Cyclin E1 in Murine and Human Liver Cancer: A Promising Target for Therapeutic Intervention during Tumour Progression.

Cyclin E1 (CCNE1) is a regulatory subunit of Cyclin-dependent kinase 2 (CDK2) and is thought to control the transition of quiescent cells into cell cycle progression. Recently, we identified CCNE1 and CDK2 as key factors for the initiation of hepatocellular carcinoma (HCC). In the present study, we dissected the contributions of CCNE1 and CDK2 for HCC progression in mice and patients. Therefore, we generated genetically modified mice allowing inducible deletion of Ccne1 or Cdk2. After initiation of HCC, using the hepatocarcinogen diethylnitrosamine (DEN), we deleted Ccne1 or Cdk2 and subsequently analysed HCC progression. The relevance of CCNE1 or CDK2 for human HCC progression was investigated by in silico database analysis. Interventional deletion of Ccne1, but not of Cdk2, substantially reduced the HCC burden in mice. Ccne1-deficient HCCs were characterised by attenuated proliferation, impaired DNA damage response and downregulation of markers for stemness and microinvasion. Additionally, the tumour microenvironment of Ccne1-deficient mice showed a reduction in immune mediators, myeloid cells and cancer-associated fibroblasts. In sharp contrast, Cdk2 was dispensable for HCC progression in mice. In agreement with our mouse data, CCNE1 was overexpressed in HCC patients independent of risk factors, and associated with reduced disease-free survival, a common signature for enhanced chromosomal instability, proliferation, dedifferentiation and invasion. However, CDK2 lacked diagnostic or prognostic value in HCC patients. In summary, CCNE1 drives HCC progression in a CDK2-independent manner in mice and man. Therefore, interventional inactivation of CCNE1 represents a promising strategy the treatment of liver cancer.

Differential effects of selective- and pan-PPAR agonists on experimental steatohepatitis and hepatic macrophages☆.

BACKGROUND & AIMS: Peroxisome proliferator-activated receptors (PPARs) are essential regulators of whole-body metabolism, but also modulate inflammation in immune cells, notably macrophages. We compared the effects of selective PPAR agonists to those of the pan-PPAR agonist lanifibranor in non-alcoholic fatty liver disease (NAFLD), and studied isoform-specific effects on hepatic macrophage biology. METHODS: Lanifibranor or selective PPARα (fenofibrate), PPARγ (pioglitazone) and PPARδ (GW501516) agonists were therapeutically administered in choline-deficient, amino acid-defined high-fat diet (CDAA-HFD)- and Western diet (WD)-fed mouse models of NAFLD. Acute liver injury was induced by carbon tetrachloride (CCl4). The role of PPARs on macrophage functionality was studied in isolated hepatic macrophages, bone marrow-derived macrophages stimulated with palmitic acid, and circulating monocytes from patients with NAFLD. RESULTS: Lanifibranor improved all histological features of steatohepatitis in CDAA-HFD-fed mice, including liver fibrosis, thereby combining and exceeding specific effects of the single PPAR agonists. Its potent anti-steatotic efficacy was confirmed in a 3D liver biochip model with primary cells. Infiltrating hepatic monocyte-derived macrophages were reduced following PPAR agonist administration, especially with lanifibranor, even after short-term treatment, paralleling improved steatosis and hepatitis. Lanifibranor similarly decreased steatosis, liver injury and monocyte infiltration in the WD model. In the acute CCl4 model, neither single nor pan-PPAR agonists directly affected monocyte recruitment. Hepatic macrophages isolated from WD-fed mice displayed a metabolically activated phenotype. Lanifibranor attenuated the accompanying inflammatory activation in both murine palmitic acid-stimulated bone marrow-derived macrophages, as well as patient-derived circulating monocytes, in a PPARδ-dependent fashion. CONCLUSION: Pan-PPAR agonists combine the beneficial effects of selective PPAR agonists and may counteract inflammation and disease progression more potently. PPARδ agonism and lanifibranor directly modulate macrophage activation, but not infiltration, thereby synergizing with beneficial metabolic effects of PPARα/γ agonists. LAY SUMMARY: Peroxisome proliferated-activated receptors (PPARs) are essential regulators of metabolism and inflammation. We demonstrated that the pan-PPAR agonist lanifibranor ameliorated all aspects of non-alcoholic fatty liver disease in independent experimental mouse models. Non-alcoholic fatty liver disease and fatty acids induce a specific polarization status in macrophages, which was altered by lanifibranor to increase expression of lipid handling genes, thereby decreasing inflammation. PPAR isoforms have differential therapeutic effects on fat-laden hepatocytes, activated hepatic stellate cells and inflammatory macrophages, supporting the clinical development of pan-PPAR agonists.