Background/Purpose: Lysyl oxidase (LOX) is a copper-dependent amine oxidase whose primary function is the covalent crosslinking of collagens in the extracellular matrix (ECM). Fibrosis is one of the important causes of morbidity and mortality in fibroproliferative disorders such as Systemic sclerosis (SSc). It was recently reported that LOX levels are increased in sera of SSc patients and associated with dermal fibrosis. In this study, we investigated the role of LOX in the pathophysiology of SSc.

Methods: LOX expression was examined in lung fibroblasts from 9 healthy controls (HC), 21 SSc patients, and 10 idiopathic pulmonary fibrosis (IPF) patients by real-time PCR. LOX was detected in HC and SSc lung tissues by immunohistochemistry. In vivo, LOX levels were quantified in lungs and sera of mice treated with bleomycin in combination with an endostatin-derived peptide that ameliorates fibrosis. LOX mRNA and activity levels were measured in vivo in lung tissues and serum samples using real-time PCR, ELISA and activity assay, respectively. In vitro, LOX mRNA levels and activity were measured in primary normal human lung fibroblasts treated with TGF-β and endostatin-derived peptide. To examine the effect of LOX, primary lung fibroblasts and lung tissues were treated with recombinant LOX with or without the inhibitor, β-aminopropionitrile (BAPN), and the expression levels of ECM (collagen and fibronectin) and pro-fibrotic factors (IL-6 and TGF-β) were measured by real-time PCR, ELISA, immunoblotting, and hydroxyproline assay.

Results: : LOX mRNA and protein levels were significantly increased in lung fibroblasts of SSc patients compared to HC and IPF patients. Interestingly, the highest levels of LOX were detected in SSc patients with pulmonary fibrosis. In vivo, bleomycin significantly induced LOX mRNA expression in lung tissues. Further, bleomycin increased LOX protein and activity levels in the circulation, suggesting that circulating LOX protein and activity levels paralleled levels in lung tissues. Amelioration of bleomycin-induced pulmonary fibrosis by endostatin peptide reduced LOX expression and activity. In vitro, TGF-β induced collagen and fibronectin production, LOX expression and activity. Endostatin peptide abrogated these effects. Recombinant LOX induced collagen and fibronectin production in vitro in lung fibroblasts and ex vivo in human lung tissues maintained in organ culture. The inhibition of LOX catalytic activity by BAPN failed to abrogate LOX-induced ECM production. LOX increased the production of IL-6 but not TGF-β in vitro and ex vivo.

Conclusion: LOX expression and activity correlated with fibrosis ex vivo, in vitro, and in vivo. LOX induced ECM production in vitro and ex vivo via upregulation of IL-6. Therefore, measuring LOX levels and activity serves as a novel biomarker for fibroproliferative disorders and for monitoring response to therapy, and LOX likely plays a direct pathogenic role in SSc independently of its crosslinking function.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/lysyl-oxidase-induces-fibrosis-via-upregulation-of-il-6-and-serves-as-a-biomarker-to-monitor-response-to-therapy/