Promotion of Myofibroblast Differentiation and Tissue Fibrosis by the Leukotriene B₄–Leukotriene B₄ Receptor Axis in Systemic Sclerosis

Abstract

Objective. To investigate the role of the inflammatory lipid mediator leukotriene B 4 (LTB 4 ) and its receptor, BLT1, in the development and progression of systemic sclerosis (SSc).Methods. Serum levels of LTB 4 were compared in 64 patients with SSc and 80 healthy controls. Skin and lung tissue sections from patients with SSc and healthy donors were immunostained for leukotriene A 4 hydrolase (LTA 4 H), the critical enzyme for LTB 4 synthesis, and BLT1, in combination with different cell markers. In mouse models of SSc using bleomycin or angiotensin II challenge or immunization with the DNA topoisomerase I, genetic or pharmacologic interruption of the LTB 4 -BLT1 axis in mice was carried out to assess its effects on systemic disease features and myofibroblast markers. Immunoblotting was performed to examine the signaling pathway in fibroblasts and endothelial cells following stimulation with LTB 4 or with serum from SSc patients.Results. Serum LTB 4 levels were 44.93% higher in patients with SSc than in matched healthy controls (mean ± SD 220.3 ± 74.75 pg/ml versus 152.0 ± 68.05 pg/ml; P < 0.0001), and this was associated with the patient subsets of SSc-associated interstitial lung disease and diffuse cutaneous SSc. Levels of LTA 4 H and BLT1 were increased in lesional areas of the skin and lungs of SSc patients, and both were abundant in myofibroblasts and endothelial cells. Interruption of the LTB 4 -BLT1 axis in mouse models of SSc significantly mitigated dermal and pulmonary fibrosis, with 54.00% and 52.65% fewer α-smooth muscle actin-positive myofibroblasts accumulating in the skin and lungs of mice, respectively, after bleomycin challenge. Immunoblotting of cultures with recombinant LTB 4stimulated fibroblasts and endothelial cells or with serum from SSc patients showed that fibroblast-myofibroblast and endothelial-mesenchymal transitions were promoted via BLT1, and that this was dependent on activation of the phosphatidylinositol 3-kinase (PI3K)/Akt/mechanistic target of rapamycin (mTOR) pathway but independent of the release of transforming growth factor β (TGFβ) by fibroblasts or endothelial cells.Conclusion. The LTB 4 -BLT1 axis may contribute to fibrosis in SSc by directly promoting myofibroblast differentiation via the PI3K/Akt/mTOR pathway, and this appears to operate independently of autocrine secretion of TGFβ.

New Insights into Profibrotic Myofibroblast Formation in Systemic Sclerosis: When the Vascular Wall Becomes the Enemy

“…Recently, dermal ECs explanted from KLF5+/−; Fli1+/− mice, a new animal model resembling the fundamental pathologic features of SSc, were reported not only to be defective in performing in vitro angiogenesis, but also to have a reduced expression of VE-cadherin and CD31, suggesting the occurrence of EndoMT, as observed in SSc-affected ECs, and highlighting that a deficiency of KLF5 transcription factor may be another important trigger of this process [ 59 ]. SSc-related EndoMT has been recently found to be induced also by oncostatin M, a member of the IL-6 family, and the inflammatory lipid mediator leukotriene B4, whose expression levels are increased in SSc [ 60 , 61 ]. In particular, oncostatin M was able to induce EndoMT-like morphologic changes in healthy dermal microvascular ECs, while leukotriene B4 promoted EndoMT in human umbilical vein ECs via the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of the rapamycin (mTOR) pathway, independently of TGF-β1 release [ 61 ].…”

“…SSc-related EndoMT has been recently found to be induced also by oncostatin M, a member of the IL-6 family, and the inflammatory lipid mediator leukotriene B4, whose expression levels are increased in SSc [ 60 , 61 ]. In particular, oncostatin M was able to induce EndoMT-like morphologic changes in healthy dermal microvascular ECs, while leukotriene B4 promoted EndoMT in human umbilical vein ECs via the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of the rapamycin (mTOR) pathway, independently of TGF-β1 release [ 61 ]. A putative contribution in EndoMT induction has additionally been attributed, even if only in experimental scleroderma, to abnormal fibrillin-1 expression and chronic oxidative stress in the tight-skin mouse model of SSc [ 62 ] and to interferon regulatory factor 5 (IRF5), as demonstrated by the fact that EndoMT is inhibited in the IRF5 knockout mouse model [ 63 ].…”

Endothelial-to-mesenchymal transition in systemic sclerosis

“…Recently, it has been reported that, in dermal SSc‐ECs, the treatments with OSM or IL‐6 + sIL‐6R stimulate proinflammatory genes, together with genes related to EndMT [166]. The serum levels of the leucotriene (LT) B4, an inflammatory lipid mediator, are increased in patients with diffuse cutaneous SSc and ILD and promote EndMT via the phosphatidylinositol 3‐kinase (PI3K)/protein kinase B (AKT)/mammalian target of the rapamycin (mTOR) pathway, independently of TGF‐β release [167].…”

Therapeutic Effects of Specialized Pro-Resolving Lipids Mediators on Cardiac Fibrosis via NRF2 Activation

“…However, while RvE1 promotes NADPH oxidase-mediated ROS production through the BLT1 receptor, RvE2 and RvE3 do not exhibit this effect [134]. The activation of BLT1 via LTB4 is involved in promoting fibrosis [135][136][137]. Research on whether fibrosis is inhibited by RvE1, a ligand related to the termination of inflammation of BLT1, has not yet been conducted.…”