Knockdown of LOX and IL1B Suppresses Tumor Growth on Aged ECM
To investigate ECM-mediated tumor progression with age, we identified several targets known to literature to be upregulated within the aged environment and related to tumor growth and metastasis: IL1B31,32, P4HA133,34, and LOX13,35. We first generated and validated stable knockdown cell lines (shIL1B, shLOX, and shP4HA1) from MCF10A DCIS.com cells (Fig. 1A, 1C, 1E). From this, we engineered a novel hybridized mouse model by utilizing decellularized ECM (dECM) derived from aged (24–48 months) murine mammary glands of C57BL/6 mice and implanted them into young Rag1−/− mice. Before implantation, dECM were seeded with a control (shNT) and one of the knockdown cell lines. The mice were split into two groups with reversed implantation locations to eliminate the influence of environmental variation on tumor growth between the left and right sides of the mammary fat pad (Fig. 1A). This experimental design allowed for a direct comparison of the tumor growth between control and knockdown tumors under controlled conditions. Each line was seeded onto aged dECM and implanted into young Rag1−/− mice mammary fat pad, with matched shNT controls implanted on the opposing side. After 6 weeks, mice were sacrificed, and tumors were excised for analysis. shLOX tumors were significantly smaller than shNT (n = 9, p = 0.0135). IL1B knockdown resulted in a non-significant decrease in tumor volume compared to control (Fig. 1D). Interestingly, P4HA1 knockdown increased tumor volume compared to control, suggesting a potentially context-dependent role in the aged ECM (Fig. 1F)
LOX Knockdown Suppresses Pro-Metastatic Cell State and Gene Expression
As LOX was found to be the most impactful and consistent on tumor development and growth, we next processed shLOX and their respective shNT tumors for scRNA-sequencing (scRNA-seq) analysis to further study the differences at a transcriptomic level. Before scRNA-seq processing, CD11b+ (myeloid cells) and CD11b− (tumor and stromal cells) were separated using magnetic bead enrichment and sequenced separately. scRNA-sequencing was performed on both the tumor (Fig. 2, Table S1) and immune (Fig. S1, Table S2) cells.
Analysis of the tumor cells revealed 4 distinct clusters and their respective marker and significant genes (Fig. 2A-C) – Cluster 0: stressed, Cluster 1: ECM/remodeling, Cluster 2: invasive, Cluster 3: cancer-associated fibroblasts (CAFs). LOX knockdown led to reduced relative proportions of Clusters 0 and 2 and an increase in Cluster 1. Cluster 0 exhibits high expression of LINC01091 and HSD11B1-AS1, both of which are long noncoding RNAs, the latter having known regulatory roles in cancer.36–40 In addition, high expression of ABCC2 and TMCC3 have been linked to chemoresistance and stress response.41–43 Cluster 1 expresses markers such as MUC5B, MUC16, and MMP7, indicating that this cluster has ECM remodeling and mucin production roles.44–47 Cluster 2 expresses several invasion and migration related genes, such as RASA3 and MMP3,48–50 indicating a pro-metastatic program. In addition, this cluster is marked by immune evasion and hypoxic response genes such as HLA-F-AS1 and HIF1A-AS3, respectively.51–55 Cluster 3 CAFs are marked by ECM genes such as COL5A1, AEBP1, and FBLN2. Within the shLOX group, the relative frequencies of Clusters 0 and 2 decreased, whereas the relative frequency of Cluster 1 increased (Fig. 2B). This shift suggests that after intracellular LOX knockdown, the transcriptional programs with roles in tumor progression and metastasis are suppressed, whereas those responsible for ECM structure are enhanced.
LOX Knockdown Alters Oncogenic and Hallmark Signaling Pathways
The transcriptional differences between shLOX and shNT were further examined through differential gene expression (DEG) analysis (Table S3). Genes such as HMGA256 and KCNMA157, which have been shown to be linked to various cancer types as biomarkers for cancers initiation and invasion, were significantly downregulated on shLOX tumors (Fig. 2D). Gene Set Enrichment Analysis (GSEA) of the Oncogenic Gene Set (Table S4-S5) showed downregulation of JAK, Wnt, and YAP signaling – mechanosensitive pathways which are often dysregulated in cancerous environments.58–60 BRCA161 and ATM62 – DNA repair pathways – were also downregulated. Interestingly, KRAS-related gene-sets were elevated in both shNT and shLOX groups, suggesting that LOX may play a dual role in modulating this pathway in the aged microenvironment (Fig. 2E). Further analysis with the Hallmark Gene Set (Table S6-S7) demonstrated suppression of epithelial-to-mesenchymal-transition (EMT) and inflammatory pathways while showing upregulation of pathways related to cholesterol homeostasis and reactive oxygen species (ROS) (Fig. 2F). Together, these results indicate that the knockdown of LOX is capable, within the aged environment, of suppressing pathways beneficial for tumor proliferation, invasion and stress response, supporting its role as a key effector of matrix-induced tumor progression.
Aged ECM Drives Tumor Growth In Vivo
With observed differential tumor growth between control and knockdown cell lines in our model, we next aimed to isolate the independent contribution of the aged ECM to tumor progression. Rather than assessing with differential cell lines, we utilized decellularized ECM (dECM) derived from young (2–4 months) and aged (24–48 months) murine mammary glands of C57BL/6 mice and implanting them into young Rag1−/− mice. Before implantation, dECM were seeded with normal MCF10A DCIS.com cells. The mice were split into two groups with reversed implantation locations to eliminate the influence of environmental variation on tumor growth between the left and right sides of the mammary fat pad (Fig. 3A-B). This experimental design allowed for a direct comparison of the tumor growth in young vs. aged environments under controlled conditions. After, tumors on the aged dECM were found to be significantly larger, with an average volume of 327 ± 132 mm3, compared to those on the young dECM, which averaged 162 ± 60 mm3 (p = 0.0032, n = 10) (Fig. 3C-D). Further histological analysis with hematoxylin and eosin (H&E) staining confirmed an approximate 14% average increase in tumorigenic region in tumors from the aged sides (Fig. 3E-F), confirming that the aged ECM independently promotes tumor growth and tissue invasion.
Aged ECM Enriches Invasive and Inflammatory Phenotype
To better understand the underlying transcriptomic mechanisms and cell populations contributing to tumor growth and development between the groups, scRNA-seq was performed on the excised tumors (Fig. 4, Fig. S2, and Table S8). Transcriptomic analysis revealed 12 distinct cell clusters and their defining marker genes (Fig. 4A-C). These clusters exhibited a differential proportional distribution between tumors grown in young vs. aged ECM conditions.
Clusters 0, 1, and 11 were found to be most expanded within the aged matrices and were mostly related to ECM remodeling, cell cycle regulators, and genome regulators, respectively. Cluster 0 showed upregulation of genes such as KRT2363,64, DNER65,66, and TSPAN267,68, which are typically associated with cell structure and various cellular processes. These genes have been previously implicated as cancer biomarkers where they play a role in cell migration, invasion, downstream gene expression, and metastasis. Cluster 1 displayed strong expression of mitotic and cell cycle regulators, including CEP5569,70, HMMR71,72, and CCNA273,74, as well as microtubule-associated proteins – such as KIF2C75,76 and KIF18B77,78. Together, these indicate a highly proliferative transcriptional state within the aged ECM. Finally, Cluster 11 was enriched in genes relating to DNA replication and cell cycle regulators such as MCM679,80, E2F181,82, WDR7683,84, and DTL85,86. This further suggests that the aged ECM promotes aberrant replication and proliferative signaling, with many of the upregulated genes having been previously linked to cancer-associated cell cycle dysregulation and proliferative biomarkers. Conversely, within the young ECM Clusters 3, 5, and 7 were found to be enriched with roles in ion channel and immune regulation, ECM stability, and tumor suppression genes. Cluster 3 was highly defined by the expression of various ion channel regulators such as KCNMA187,88 and TRPV389,90, alongside immune regulatory genes including PLCG291,92 and C6orf14193,94, suggesting a role in maintenance of coordinated cellular communication and response and immune-mediated tumor suppression. Cluster 5 exhibited high level of ECM stability and remodeling genes – MMP195, MMP996, MMP1097, indicating ECM remodeling within the young ECM. While these MMPs are frequently associated with cancer initiation and invasion98–101, in the young ECM they marked a state of remodeling redirected toward tumor suppression rather than initiation. Finally, Cluster 7 was enriched in tumor suppressor genes, including CLCA2102,103, CADM3104,105, further supporting that the young ECM fosters a microenvironment that limits tumor progression. Complementing the cluster-specific findings, volcano plot analyses of significant genes (Fig. S3) revealed that the aged ECM biases dual-function genes toward tumor-suppressive programs. Notably, DDIT4106, typically characterized as a biomarker of cancer progression107 but also documented as a tumor suppressor108, was upregulated, demonstrating the influence of the aged microenvironment’s role in tumor development. Similarly, the aged ECM showed enrichment of C5orf46109, a gene correlated with poor prognosis due to its role in driving malignant phenotypes and reshaping the immune landscape toward tumor support110 (Fig. 4D). To further contextualize these changes, we investigated AIF-1 – a gene previously implicated in breast cancer development, progression, and metastasis – which revealed an average 12% expression in tumors gown on aged ECM, compared to 8% in young, within the same host model (Fig. 4E-F). Up-regulation of AIF-1 suggests tumor cells adopt a unique inflammatory signature in the aged microenvironment. Together, the age-respective profiles suggest that the aged ECM promotes a tumor-permissive environment, contrasting the young ECM’s immune regulation and tumor suppression.