The pathological significance of LOXL2 in pre-metastatic niche formation of HCC and its related molecular mechanism

Abstract Background: The mechanisms underlying the contribution of primary tumor to pre-metastatic niche formation remains largely unknown in HCC. We previously reported that the released Lysyl oxidase like 2 (LOXL2) from HCC cells under higher stiffness stimulation facilitated the formation of lung pre-metastatic niche. Here we further clarified the pathological role of LOXL2 in promoting lung pre-metastatic niche formation in HCC and its relevant molecular mechanism. Methods: Lung pre-metastatic niche nude mouse model and LOXL2-overexpressed xenograft HCC models were respectively developed to validate the significance of LOXL2 in pre-metastatic niche formation and pulmonary metastasis. Simultaneously, a gel-based cell culture system mirroring lung tissue stiffness in normal and pathological state was constructed to investigate the underlying mechanism of LOXL2-induced pre-metastatic niche formation.Results: LOXL2 by tail vein injection had obvious inducting effects on CD11b+/CD45+ BMDCs recruitment and fibronectin expression in lung tissue during the development of lung pre-metastatic niche. Tumor-secreted LOXL2 also promoted the occurrence of pulmonary metastasis and the number of metastasis lesions remarkably in LOXL2-overexpressed xenograft HCC models. Applying a gel-based cell culture system, we discovered that LOXL2 and LOXL2-caused matrix stiffening all upregulated the expressions of MMP9 and fibronectin in lung fibroblasts significantly, but little effect on MMP2 expression. Moreover, the activation of PI3K-AKT pathway participated in the regulation of LOXL2-upregulated fibronectin. Additionally, LOXL2 and LOXL2-caused matrix stiffening also increased the number of adherent HCC cells evidently, as well as the expression of chemokine CXCL2. Clinical data analysis demonstrated that HCC patients in High-LOXL2 group had higher ratio of microvascular invasion (OR=10.563, P=0.005) and tumor recurrence (OR=8.556, P=0.013) than HCC patients in Low-LOXL2 group, also revealing a significance of LOXL2 in HCC progression and unfavorable outcomeConclusion: Primary tumor-released LOXL2 contributes to the formation of lung pre-metastatic niche and the occurrence of lung metastasis. LOXL2 and LOXL2-caused matrix stiffening work together to induce pre-metastatic niche formation through influencing matrix remodeling and cell colonization. This study sheds light on the pathological significance of LOXL2 in lung pre-metastatic niche formation in HCC, also implicates a new intervention approach for HCC metastasis through reversal of lung pre-metastatic niche.