Roles of the chemokine CXCL12 in liver inflammation and fibrosis associated with HIV infection

Chronic liver disease (CLD) has emerged as a leading cause of morbidity and mortality among people living with HIV (PLWH). Liver fibrosis, a hallmark of CLD progression, is influenced by various cellular and soluble mediators produced in the liver environment. Particularly, the chemokine CXCL12/CXCR4/CXCR7 axis has been implicated in multiple inflammatory and fibrotic diseases; however, its specific contribution to the pathogenesis of HIV-associated liver fibrosis remains largely unclear. This study aimed to investigate the role of CXCL12 in liver fibrosis among PLWH, using a comprehensive proteomic approach, complemented with in vitro models of hepatocyte death and monocyte-to-macrophage differentiation to elucidate the underlying molecular mechanisms. Serum samples from HIV-infected patients with and without liver fibrosis were analyzed using mass spectrometry-based proteomics. Bioinformatic analysis revealed 1,289 proteins differentially expressed, of which 48 were identified as upregulated or downregulated in the samples with liver fibrosis. Protein-protein interaction (PPI) analysis in the STRING 12.0 database identified six proteins, CLU, CINP, APOE, KHSRP, SNW1 and CFHR5, which are involved in the fibrogenic TGF-α/SMAD signaling networks. Importantly, PPI analysis also predicted interactions between the CXCL12 signaling axis and APOE/CLU, within the networks associated with lipid metabolism and apoptosis. Furthermore, serum validation showed a tendency toward lower clusterin (CLU) levels and significantly elevated CXCL12 levels in patients with liver fibrosis. An in vitro model of caspase-dependent apoptosis in HegG2 cells, induced by cycloheximide (CHX) and tumor necrosis factor-α (TNF-α), was employed to investigate the regulation of CXCL12, CXCR4 and CXCR7, and CLU under chronic inflammatory conditions. In this model, increased intracellular CXCL12 expression and decreased clusterin secretion were observed. Inhibitor studies demonstrated that these changes were mediated via the caspase and phosphoinositide 3-kinase (PI3K) signaling pathways. Furthermore, CXCR4 signaling was required for CLU secretion, potentially mediated via PI3K activation pathway. This suggests a novel mechanistic interplay between inflammatory CXCL12/CXCR4 signaling and CLU-mediated cytoprotective pathways. Additionally, an in vitro model of monocyte-to-macrophage differentiation in THP-1 cells, induced by phorbol 12-myristate 13-acetate (PMA), was utilized to examine the involvement of CXCL12/CXCR4/CXCR7 system in the establishment of macrophage phenotypes. The data indicated alterations in the CXCL12, CXCR4 and CXCR7 expression profiles in differentiated cells, potentially contributing to macrophage differentiation. Interestingly, paracrine activation of differentiated cells with CXCL12 induced the transcriptional expression of the fibrogenic TGF-β, potentially suggesting its pathogenic role in macrophage-mediated inflammation and fibrosis. In conclusion, this study underscores the significance of the chemokine CXCL12 system in the pathogenesis of liver fibrosis in PLWH. These findings highlight CXCL12 signaling as a key mediator of hepatocyte/macrophage-driven inflammation and fibrogenesis and suggest that the CXCL12/CXCR4 pathway is a potential diagnostic and therapeutic target of liver diseases.