Tobias Puengel

Macrophages are key regulators of liver fibrosis progression and regression in nonalcoholic steatohepatitis (NASH). Liver macrophages comprise resident phagocytes, Kupffer cells, and monocyte‐derived cells, which are recruited through the chemokine receptor C‐C motif chemokine receptor 2 (CCR2). We aimed at elucidating the therapeutic effects of inhibiting monocyte infiltration in NASH models by using cenicriviroc (CVC), an oral dual chemokine receptor CCR2/CCR5 antagonist that is under clinical evaluation. Human liver tissues from NASH patients were analyzed for CCR2 + macrophages, and administration of CVC was tested in mouse models of steatohepatitis, liver fibrosis progression, and fibrosis regression. In human livers from 17 patients and 4 controls, CCR2 + macrophages increased parallel to NASH severity and fibrosis stage, with a concomitant inflammatory polarization of these cluster of differentiation 68 + , portal monocyte‐derived macrophages (MoMF). Similar to human disease, we observed a massive increase of hepatic MoMF in experimental models of steatohepatitis and liver fibrosis. Therapeutic treatment with CVC significantly reduced the recruitment of hepatic Ly‐6C + MoMF in all models. In experimental steatohepatitis with obesity, therapeutic CVC application significantly improved insulin resistance and hepatic triglyceride levels. In fibrotic steatohepatitis, CVC treatment ameliorated histological NASH activity and hepatic fibrosis. CVC inhibited the infiltration of Ly‐6C + monocytes, without direct effects on macrophage polarization, hepatocyte fatty acid metabolism, or stellate cell activation. Importantly, CVC did not delay fibrosis resolution after injury cessation. RNA sequencing analysis revealed that MoMF, but not Kupffer cells, specifically up‐regulate multiple growth factors and cytokines associated with fibrosis progression, while Kupffer cells activated pathways related to inflammation initiation and lipid metabolism. Conclusion : Pharmacological inhibition of CCR2 + monocyte recruitment efficiently ameliorates insulin resistance, hepatic inflammation, and fibrosis, corroborating the therapeutic potential of CVC in patients with NASH. (H epatology 2018;67:1270‐1283)

Acetaminophen (APAP, paracetamol) poisoning is a leading cause of acute liver failure (ALF) in humans and induces hepatocyte necrosis, followed by activation of the innate immune system, further aggravating liver injury. The role of infiltrating monocytes during the early phase of ALF is still ambiguous. Upon experimental APAP overdose in mice, monocyte‐derived macrophages (MoMFs) massively accumulated in injured liver within 12‐24 hours, whereas the number of tissue‐resident macrophages (Kupffer cells) decreased. Influx of MoMFs is dependent on the chemokine receptor, chemokine (C‐C motif) receptor 2 (CCR2), given that Ccr2−/− mice display reduced infiltration of monocytes and attenuated liver injury post‐APAP overdose at early time points. As evidenced by intravital multiphoton microscopy of Ccr2 reporter mice, CCR2 + monocytes infiltrate liver as early as 8‐12 hours post‐APAP overdose and form dense cellular clusters around necrotic areas. CCR2 + MoMFs express a distinct pattern of inflammatory, but also repair‐associated, genes in injured livers. Adoptive transfer experiments revealed that MoMFs primarily exert proinflammatory functions early post‐APAP, thereby aggravating liver injury. Consequently, early pharmacological inhibition of either chemokine (C‐C motif) ligand (CCL2; by the inhibitor, mNOX‐E36) or CCR2 (by the orally available dual CCR2/CCR5 inhibitor, cenicriviroc) reduces monocyte infiltration and APAP‐induced liver injury (AILI) in mice. Importantly, neither the early nor continuous inhibition of CCR2 hinder repair processes during resolution from injury. In line with this, human livers of ALF patients requiring liver transplantation reveal increased CD68 + hepatic macrophage numbers with massive infiltrates of periportal CCR2 + macrophages that display a proinflammatory polarization. Conclusion : Infiltrating monocyte‐derived macrophages aggravate APAP hepatotoxicity, and the pharmacological inhibition of either CCL2 or CCR2 might bear therapeutic potential by reducing the inflammatory reaction during the early phase of AILI. (H epatology 2016;64:1667‐1682)

OBJECTIVE: Bone marrow-derived myeloid cells accumulate in the liver as monocytes and macrophages during the progression of obesity-related non-alcoholic fatty liver disease (NAFLD) to steatohepatitis (NASH). Myeloid cells comprise heterogeneous subsets, and dietary overnutrition may affect macrophages in the liver and bone marrow. We therefore aimed at characterising in depth the functional adaptations of myeloid cells in fatty liver. DESIGN: We employed single-cell RNA sequencing to comprehensively assess the heterogeneity of myeloid cells in the liver and bone marrow during NAFLD, by analysing C57BL/6 mice fed with a high-fat, high-sugar, high-cholesterol 'Western diet' for 16 weeks. We also characterised NAFLD-driven functional adaptations of macrophages in vitro and their functional relevance during steatohepatitis in vivo. RESULTS: Single-cell RNA sequencing identified distinct myeloid cell clusters in the liver and bone marrow. In both compartments, monocyte-derived populations were largely expanded in NASH-affected mice. Importantly, the liver myeloid compartment adapted a unique inflammatory phenotype during NAFLD progression, exemplarily characterised by downregulated inflammatory calprotectin (S100A8/A9) in macrophage and dendritic cell subsets. This distinctive gene signature was also found in their bone marrow precursors. The NASH myeloid phenotype was principally recapitulated by in vitro exposure of bone marrow-derived macrophages with fatty acids, depended on toll-like receptor 4 signalling and defined a characteristic response pattern to lipopolysaccharide stimulation. This imprinted and stable NASH myeloid immune phenotype functionally determined inflammatory responses following acute liver injury (acetaminophen poisoning) in vivo. CONCLUSION: Liver myeloid leucocytes and their bone marrow precursors adapt a common and functionally relevant inflammatory signature during NAFLD progression.