Macrophages direct cancer cells through a LOXL2-mediated metastatic cascade in pancreatic ductal adenocarcinoma

Abstract

ObjectiveThe lysyl oxidase-like protein 2 (LOXL2) contributes to tumour progression and metastasis in different tumour entities, but its role in pancreatic ductal adenocarcinoma (PDAC) has not been evaluated in immunocompetent in vivo PDAC models.DesignTowards this end, we used PDAC patient data sets, patient-derived xenograft in vivo and in vitro models, and four conditional genetically-engineered mouse models (GEMMS) to dissect the role of LOXL2 in PDAC. For GEMM-based studies, K-Ras+/LSL-G12D;Trp53LSL-R172H;Pdx1-Cre mice (KPC) and the K-Ras+/LSL-G12D;Pdx1-Cre mice (KC) were crossed with Loxl2 allele floxed mice (Loxl2Exon2fl/fl) or conditional Loxl2 overexpressing mice (R26Loxl2KI/KI) to generate KPCL2KO or KCL2KO and KPCL2KI or KCL2KI mice, which were used to study overall survival; tumour incidence, burden and differentiation; metastases; epithelial to mesenchymal transition (EMT); stemness and extracellular collagen matrix (ECM) organisation.ResultsUsing these PDAC mouse models, we show that while Loxl2 ablation had little effect on primary tumour development and growth, its loss significantly decreased metastasis and increased overall survival. We attribute this effect to non-cell autonomous factors, primarily ECM remodelling. Loxl2 overexpression, on the other hand, promoted primary and metastatic tumour growth and decreased overall survival, which could be linked to increased EMT and stemness. We also identified tumour-associated macrophage-secreted oncostatin M (OSM) as an inducer of LOXL2 expression, and show that targeting macrophages in vivo affects Osm and Loxl2 expression and collagen fibre alignment.ConclusionTaken together, our findings establish novel pathophysiological roles and functions for LOXL2 in PDAC, which could be potentially exploited to treat metastatic disease.

LOXL2 in pancreatic tumourigenesis: the complexity of tumour–stromal crosstalk exemplified

“…Consistent with this, they found that loss of LOXL2 decreased metastasis and increased survival, primarily due to significantly less organised ECM, and reduced stiffness and mechanosignalling. Importantly, human datasets support these findings, with higher LOXL2 expression associated with decreased survival and enrichment for an EMT signature,4 suggesting that evaluation of LOXL2 targeting in the metastatic setting may be warranted.…”

“…Indeed, more generally, there has been controversy over the stroma and ECM in PDAC, and although they clearly influence disease initiation and aggressiveness, they can exhibit tumour-suppressive activity in some contexts 3. In this issue, Alonso-Nocelo et al sought to address some of these questions, investigating the role of LOXL2 in pancreatic tumourigenesis using model systems 4…”

“…There are a few differences to highlight here. In the studies by Alonso-Nocelo et al and Chen et al , LOXL2 or collagen 1 was deleted from epithelial cells or myofibroblasts, respectively, in contrast to the systemic therapeutic approach taken by Jiang et al 4–6. Interestingly, proteomic analyses have shown that while the majority of ECM proteins originate from stromal cells, tumour cell-derived ECM proteins are more clearly associated with poor prognosis 7.…”

“…Both Alonso-Nocelo et al and Chen et al also noted changes to the immune TME, which may impact on the phenotypes observed. These studies both used autochthonous models in which tumour progression and TME establishment occur spontaneously and over a longer time, while Jiang et al used a transplant model 4–6. Clearly, the choice of model system may influence study outcomes, a point underscored by the lack of LOXL2 expression in many PDAC cell lines 4.…”

“…These studies both used autochthonous models in which tumour progression and TME establishment occur spontaneously and over a longer time, while Jiang et al used a transplant model 4–6. Clearly, the choice of model system may influence study outcomes, a point underscored by the lack of LOXL2 expression in many PDAC cell lines 4. Finally, in both the Alonso-Nocelo et al ’s and the Chen et al ’s study, deletion of LOXL2 or collagen 1 occurred from birth, prior to tumour development, whereas, in the anti-LOXL2 therapeutic study conducted by Jiang et al , treatment commenced post-transplant 4–6.…”