Moderate Increase of Indoxyl Sulfate Promotes Monocyte Transition into Profibrotic Macrophages

Abstract

ObjectiveThe uremic toxin Indoxyl-3-sulphate (IS), a ligand of Aryl hydrocarbon Receptor (AhR), raises in blood during early renal dysfunction as a consequence of tubular damage, which may be present even when eGFR is normal or only moderately reduced, and promotes cardiovascular damage and monocyte-macrophage activation. We previously found that patients with abdominal aortic aneurysms (AAAs) have higher CD14+CD16+ monocyte frequency and prevalence of moderate chronic kidney disease (CKD) than age-matched control subjects. Here we aimed to evaluate the IS levels in plasma from AAA patients and to investigate in vitro the effects of IS concentrations corresponding to mild-to-moderate CKD on monocyte polarization and macrophage differentiation.MethodsFree IS plasma levels, monocyte subsets and laboratory parameters were evaluated on blood from AAA patients and eGFR-matched controls. THP-1 monocytes, treated with IS 1, 10, 20 μM were evaluated for CD163 expression, AhR signaling and then induced to differentiate into macrophages by PMA. Their phenotype was evaluated both at the stage of semi-differentiated and fully differentiated macrophages. AAA and control sera were similarly used to treat THP-1 monocytes and the resulting macrophage phenotype was analyzed.ResultsIS plasma concentration correlated positively with CD14+CD16+ monocytes and was increased in AAA patients. In THP-1 cells, IS promoted CD163 expression and transition to macrophages with hallmarks of classical (IL-6, CCL2, COX2) and alternative phenotype (IL-10, PPARγ, TGF-β, TIMP-1), via AhR/Nrf2 activation. Analogously, AAA sera induced differentiation of macrophages with enhanced IL-6, MCP1, TGF-β, PPARγ and TIMP-1 expression.ConclusionIS skews monocyte differentiation toward low-inflammatory, profibrotic macrophages and may contribute to sustain chronic inflammation and maladaptive vascular remodeling.

Alternatively Activated (M2) Macrophage Phenotype Is Inducible by Endothelin-1 in Cultured Human Macrophages

“…This result was in accordance with several in vitro studies, indicating THP-1-derived macrophages as a well-characterized model for studying macrophage polarization [16,17,23–25]. …”

“…Human monocyte cells (THP-1 cell line, 1x10 6 cells/mL, accession number ICLC HTL97014, Cell bank Interlab Cell Line Collection, Genoa, Italy) were plated in cell culture dishes and stimulated with phorbol myristate acetate (PMA, 50ng/mL, Sigma-Aldrich, Italy) for 4 hours to induce their differentiation into macrophages (M0 macrophages), in accordance with several in vitro studies [16–18]. Once differentiated, PMA was removed and some M0 macrophages were treated for 72 hours with ET-1 (100nM, Enzo Life Science, UK) or pre-treated for 1 hour with ET A/B RA (bosentan, 10 -5 M, Actelion Pharmaceutics, Switzerland) before being stimulated with ET-1.…”

The Uremic Toxin Indoxyl Sulfate Accelerates Thrombotic Response after Vascular Injury in Animal Models

“…Beyond this, microparticles can be released by monocyte/macrophages during inflammatory state. It is not excluded that IS, which promotes inflammatory state and differentiation of monocyte into macrophages with pro-fibrotic phenotype, can also enhance release of this kind of microparticles [ 33 , 34 ].…”

The Impact of Uremic Toxins on Cerebrovascular and Cognitive Disorders

“…In addition, in a recent study performed on in vitro THP-1 cell cultures, IS was reported to promote CD163 expression and transition to macrophages with the hallmarks of classical M1 (IL-6, CCL2, COX2) and alternative M2 (IL-10, PPARγ, TGF-β, TIMP-1) phenotypes via AhR/Nrf2 activation. The authors concluded that IS may skew monocyte differentiation toward low-inflammatory, profibrotic macrophages and may therefore contribute to persistence of chronic inflammation [ 128 ]. Post-stroke intracerebral monocyte recruitment following BBB disruption largely contributes to increased cerebral inflammation and subsequent aggravation of ischemic lesions.…”