Endothelial‐derived thrombospondin‐1 promotes macrophage recruitment and apoptotic cell clearance

Abstract

Rapid apoptotic cell engulfment is crucial for prevention of inflammation and autoimmune diseases and is conducted by special immunocompetent cells like macrophages or immature dendritic cells. We recently demonstrated that endothelial cells (ECs) also participate in apoptotic cell clearance. However, in contrast to conventional phagocytes they respond with an inflammatory phenotype. To further confirm these pro-inflammatory responses human ECs were exposed to apoptotic murine ECs and changes in thrombospondin-1 (TSP-1) expression and in activation of intracellular signalling cascades were determined by real-time qPCR, immunoblotting and immunocytochemistry. Human primary macrophages or monocytic lymphoma cells (U937) were incubated with conditioned supernatant of human ECs exposed to apoptotic cells and changes in activation, migration and phagocytosis were monitored. Finally, plasma levels of TSP-1 in patients with anti-neutrophil cytoplasmic antibody(ANCA)-associated vasculitis (AAV) were determined by ELISA. We provided evidence that apoptotic cells induce enhanced expression of TSP-1 in human ECs and that this increase in TSP-1 is mediated by the mitogen-activated protein kinases (MAPK) ERK1 and 2 and their upstream regulators MEK and B-Raf. We also showed that plasma TSP-1 levels are increased in patients with AAV. Finally, we showed that conditioned supernatant of ECs exposed to apoptotic cells induces pro-inflammatory responses in monocytes or U937 cells and demonstrated that increased TSP-1 expression enhances migration and facilitates engulfment of apoptotic cells by monocyte-derived macrophages or U937 cells. These findings suggest that under pathological conditions with high numbers of uncleared dying cells in the circulation endothelial-derived elevated TSP-1 level may serve as an attraction signal for phagocytes promoting enhanced recognition and clearance of apoptotic cells.

Dental Follicle Stem Cells Ameliorate Lipopolysaccharide-Induced Inflammation by Secreting TGF-β3 and TSP-1 to Elicit Macrophage M2 Polarization

“…In addition, previous studies showed that by disrupting the interaction between CD47 and CD14 on human macrophages, TSP-1 limited the activation of NF-κB/AP-1 by LPS, resulting in inhibition of inflammatory cytokine production [43]. In the present study, however, addition of neutralizing antibodies against TSP-1 to DFSC-CM had little effect on the expression levels of IL-6, TNF-α and iNOS of macrophages, which may be due to the different regulatory effects of TSP-1 in different environments [43,66,67]. Intriguingly, we found that IL-10 expression was not significantly reduced by the addition of either TGF-β3 or TSP-1 neutralizing antibodies, but IL-10 was significantly inhibited when both neutralizing antibodies were added to DFSC-CM.…”

Changes in Serum Adhesion Molecules, Chemokines, Cytokines, and Tissue Remodeling Factors in Euthyroid Women Without Thyroid Antibodies Who Are at Risk for Autoimmune Thyroid Disease: A Hypothesis on the Early Phases of the Endocrine Autoimmune Reaction

“…Apart from chemokines, the attachment of the cells to the endothelium is important for diapedesis, and after diapedesis an interaction of the cells with extracellular matrix proteins is essential (12). Vascular factors and adhesion molecules, such as integrins, vascular cell adhesion protein 1, and thrombospondin-1 (THBS1) (13), play important roles in these adhesive interactions. Evidence of the important role of chemokines and integrins has been found previously in AITD in the up-regulation of CCL2 (14) and that of soluble intercellular adhesion molecule-1 (sICAM-1 or soluble cluster of differentiation 54) in the serum of patients (15,16).…”

Markers of Vascular Damage and Repair

“…This multi-functional glycoprotein is a known endogenous inhibitor of angiogenesis 57 and modulates cell adhesion and proliferation 58 . We were able to show that apoptotic cells induce expression of TSP-1 in endothelial cells 59 and that TSP-1 facilitates engulfment of apoptotic cells by phagocytes 59 . We speculate that under pathological conditions with high numbers of un-cleared dying cells in the circulation endothelialderived elevated TSP-1 level may serve as an attraction signal for phagocytes promoting enhanced recognition and clearance of apoptotic cells.…”