Macrophage MerTK promotes profibrogenic cross-talk with hepatic stellate cells via soluble mediators

• Published in: JHEP reports Vol. 4; no. 4; p. 100444
• Main Authors: Pastore, Mirella, Caligiuri, Alessandra, Raggi, Chiara, Navari, Nadia, Piombanti, Benedetta, Di Maira, Giovanni, Rovida, Elisabetta, Piccinni, Marie-Pierre, Lombardelli, Letizia, Logiodice, Federica, Rombouts, Krista, Petta, Salvatore, Marra, Fabio
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.04.2022; Elsevier
• Subjects: Gas-6; Gastroenterology and Hepatology; liver fibrosis; M2c-like macrophages; NASH; THP-1; THP-1; NAFLD; M-CSF; PMA; CM; siRNA; HSC(s); NASH; VEGF-A; ECM; liver fibrosis; TGFβ1; Gas-6; M2c-like macrophages; KC(s); TIMP1; MerTK; conditioned medium; non-alcoholic fatty liver disease; phorbol 12-myristate 13-acetate; vascular endothelial growth factor-A; tissue inhibitor of metalloproteinase 1; transforming growth factor-β1; growth arrest-specific gene 6; hepatic stellate cells; small-interfering RNA; Myeloid-epithelial-reproductive tyrosine kinase; Kupffer cell(s); extracellular matrix; macrophage colony-stimulating factor; non-alcoholic steatohepatitis; CM, conditioned medium; Gas-6, growth arrest-specific gene 6; TGFβ1, transforming growth factor-β1; NASH, non-alcoholic steatohepatitis; siRNA, small-interfering RNA; TIMP1, tissue inhibitor of metalloproteinase 1; ECM, extracellular matrix; KC(s), Kupffer cell(s); M-CSF, macrophage colony-stimulating factor; HSC(s), hepatic stellate cells; NAFLD, non-alcoholic fatty liver disease; VEGF-A, vascular endothelial growth factor-A; MerTK, Myeloid-epithelial-reproductive tyrosine kinase; PMA, phorbol 12-myristate 13-acetate
• ISSN: 2589-5559; 2589-5559
• DOI: 10.1016/j.jhepr.2022.100444

Activation of Kupffer cells and recruitment of monocytes are key events in fibrogenesis. These cells release soluble mediators which induce the activation of hepatic stellate cells (HSCs), the main fibrogenic cell type within the liver. Mer tyrosine kinase (MerTK) signaling regulates multiple processes in macrophages and has been implicated in the pathogenesis of non-alcoholic steatohepatitis-related fibrosis. In this study, we explored if MerTK activation in macrophages influences the profibrogenic phenotype of HSCs. Macrophages were derived from THP-1 cells or differentiated from peripheral blood monocytes towards MerTK+/CD206+/CD163+/CD209- macrophages. The role of MerTK was assessed by pharmacologic and genetic inhibition. HSC migration was determined in Boyden chambers, viability was measured by the MTT assay, and proliferation was evaluated by the BrdU incorporation assay. Gas-6 induced MerTK phosphorylation and Akt activation in macrophages, and these effects were inhibited by UNC569. During polarization, MerTK+/CD206+/CD163+/CD209- macrophages exhibited activation of STAT3, ERK1/2, p38 and increased expression of VEGF-A. Activation of MerTK in THP-1 macrophages induced a secretome which promoted a significant increase in migration, proliferation, viability and expression of profibrogenic factors in HSCs. Similarly, conditioned medium from MerTK+ macrophages induced a significant increase in cell migration, proliferation, STAT3 and p38 phosphorylation and upregulation of IL-8 expression in HSCs. Moreover, conditioned medium from Gas-6-stimulated Kupffer cells induced a significant increase in HSC proliferation. These effects were specifically related to MerTK expression and activity in macrophages, as indicated by pharmacologic inhibition and knockdown experiments. MerTK activation in macrophages modifies the secretome to promote profibrogenic features in HSCs, implicating this receptor in the pathogenesis of hepatic fibrosis. Fibrosis represents the process of scarring occurring in patients with chronic liver diseases. This process depends on production of scar tissue components by a specific cell type, named hepatic stellate cells, and is regulated by interaction with other cells. Herein, we show that activation of MerTK, a receptor present in a population of macrophages, causes the production of factors that act on hepatic stellate cells, increasing their ability to produce scar tissue. [Display omitted] •MerTK, a member of the TAM family of proteins, is highly expressed in MerTK+/CD206+/CD163+/CD209- macrophages.•In these macrophages, activation of MerTK induces phosphorylation of Akt, STAT3, ERK1/2, p38 and increased expression of VEGF-A.•MerTK activation in macrophages modulates the secretome to promote the profibrogenic phenotype of human HSCs.•Profibrogenic effects of macrophages expressing high levels of MerTK were blocked by knockdown or inhibition of MerTK.