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

Mirella Pastore; Alessandra Caligiuri; Chiara Raggi; Nadia Navari; Benedetta Piombanti; Giovanni Di Maira; Elisabetta Rovida; Marie-Pierre Piccinni; Letizia Lombardelli; Federica Logiodice; Krista Rombouts; Salvatore Petta; Fabio Marra

doi:10.1016/j.jhepr.2022.100444

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

JHEP Rep. 2022 Feb 1;4(4):100444. doi: 10.1016/j.jhepr.2022.100444. eCollection 2022 Apr.

Affiliations

¹ Department of Experimental and Clinical Medicine, University of Florence, Florence Italy.
² Department of Experimental and Clinical Biomedical Sciences "Mario Serio", University of Florence, Florence Italy.
³ Department of Experimental and Clinical Medicine and Center of Excellence for Research, Transfer and High Education DENOTHE of the University of Florence, Florence Italy.
⁴ Regenerative Medicine and Fibrosis Group, Institute for Liver and Digestive Health, University College London, Royal Free Hospital, United Kingdom.
⁵ Section of Gastroenterology and Hepatology, PROMISE, University of Palermo, Palermo Italy.

Abstract

Background & aims: 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.

Methods: 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.

Results: 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.

Conclusions: MerTK activation in macrophages modifies the secretome to promote profibrogenic features in HSCs, implicating this receptor in the pathogenesis of hepatic fibrosis.

Lay summary: 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.

Keywords: CM, conditioned medium; ECM, extracellular matrix; Gas-6; Gas-6, growth arrest-specific gene 6; HSC(s), hepatic stellate cells; KC(s), Kupffer cell(s); M-CSF, macrophage colony-stimulating factor; M2c-like macrophages; MerTK, Myeloid-epithelial-reproductive tyrosine kinase; NAFLD, non-alcoholic fatty liver disease; NASH; NASH, non-alcoholic steatohepatitis; PMA, phorbol 12-myristate 13-acetate; TGFβ1, transforming growth factor-β1; THP-1; TIMP1, tissue inhibitor of metalloproteinase 1; VEGF-A, vascular endothelial growth factor-A; liver fibrosis; siRNA, small-interfering RNA.