The leukotriene B4‐leukotriene B4 receptor 1 axis promotes myofibroblast differentiation and tissue fibrosis in systemic sclerosis

OBJECTIVE: This study aimed to investigate the role of an inflammatory lipid mediator, leukotriene B4 (LTB4 ), and its receptor BLT1 in systemic sclerosis (SSc). METHODS: Serum levels of LTB4 were compared in 64 subjects with SSc and 80 healthy controls (HC). Skin and lung sections were immunostained with leukotriene A4 hydrolase (LTA4 H), the critical enzyme for LTB4 synthesis, and BLT1, in combination with different cell markers. The LTB4 -BLT1 axis was genetically or pharmacologically interrupted in mouse models of SSc induced by bleomycin or angiotensin II, or immunized with the DNA topoisomerase I. Immunoblotting was performed to examine the signaling pathway in fibroblasts and endothelial cells following stimulation with LTB4 or the serum from SSc patients. RESULTS: 44.93% higher serum LTB4 levels were detected in patients with SSc than matched HCs (220.3+/-74.75 vs 152.0+/-68.05 pg/ml, p<0.0001), associated with interstitial lung disease (ILD) and diffuse cutaneous subset. LTA4 H and BLT1 were increased in lesional skin and lung areas from SSc, and abundant in myofibroblast and endothelial cells. Interruption of the LTB4 -BLT1 axis significantly mitigated dermal and pulmonary fibrosis, with 54.00% and 52.65% fewer alpha-SMA(+) myofibroblast accumulation of skin and lungs respectively after bleomycin challenging. Recombinant LTB4 or the serum of SSc patients promoted fibroblast-myofibroblast and endothelial-mesenchymal transitions via BLT1, which was dependent on activation of the PI3K/Akt/mTOR pathway, but independent of TGF-beta release by fibroblasts or endothelial cells. CONCLUSION: The LTB4 -BLT1 axis may contribute to fibrosis in SSc by directly promoting myofibroblast differentiation via the PI3K/Akt/mTOR pathway, independently of TGF-beta autocrine secretion.