Matrix metalloproteinase 9 (MMP9) limits reactive oxygen species (ROS) accumulation and DNA damage in colitis-associated cancer.

Colitis-associated cancer (CAC) is a subtype of colon cancer that is driven by chronic inflammation and is prevalent in chronic ulcerative colitis patients. The development of CAC is associated with the inflammation-dysplasia-carcinoma pathway which is significantly different than adenoma-carcinoma pathway of sporadic colon cancer (CRC). Matrix Metalloproteinase 9 (MMP9) is a zinc-dependent endopeptidase against extracellular matrix (ECM) proteins expressed in the gastrointestinal tract during inflammation. We have previously shown that MMP9 plays a tumor suppressor role in CAC via "MMP9-Notch1-ARF-p53 axis" pathway. The aim of this study is to determine the role of MMP9 in maintaining genomic stability in CAC. Homozygous transgenic mice with constitutive-expression of MMP9 in the colonic epithelium (TgM9) with their wild-type littermates (WT) and stably transfected HCT116 cells with/without MMP9 were used for in vivo and in vitro experiments, respectively. As 'proof of concept' model, nanoparticles (NPs) loaded with MMP9 siRNA were used to examine the effect of MMP9 silencing in the colonic epithelium. In CAC, colonic epithelium of TgM9 mice exhibited lower amounts of reactive oxygen species (ROS), less DNA damage, and increased expression of mismatch repair genes compared to WTs. Our study showed that MMP9 expression correlates with the reduced ROS levels, decreased DNA damage, and upregulated mismatch repair pathway. This suggests that MMP9 expression is a natural biological way to suppress CAC by limiting ROS accumulation and DNA damage in the colon. Therefore, MMP9 inhibition could be deleterious for CAC patient.

Matrix metalloproteinase MMP9 maintains epithelial barrier function and preserves mucosal lining in colitis associated cancer.

In colitis associated cancer (CAC), chronic inflammation exposes the epithelial mucosal defensive lining to inflammatory mediators such as cytokines and anti-microbial peptides (AMPs) causing the dysbiosis of microbiota population and the dysregulation of immune response. Matrix Metalloproteinases (MMPs) are zinc dependent endopeptidases which mediate inflammation, tissue remodeling, and carcinogenesis. MMP9 is undetectable in healthy tissue, although highly upregulated during inflammation and cancer. We have previously shown that MMP9 plays a protective role in CAC opposite to its conventional role of acute inflammation and cancer mediator. In this study, we investigated the mechanistic role of MMP9 in preserving the epithelial mucosal integrity to suppress the progression of tumor microenvironment in CAC. We used transgenic mice constitutively expressing MMP9 in colonic epithelium (TgM9) as an in vivo model and intestinal cell line CaCo2BBE as an in vitro model. We induced CAC with three cycles of dextran sodium sulfate (DSS). We observed that MMP9 expression in colonic epithelium maintains the microbiota. We also observed that MMP9 mediates pro-inflammatory cytokine levels and AMPs but suppresses IL-22 resulting in lower levels of REG3-g and S100A8 AMPs. We also found that MMP9 maintains an efficient barrier function and the integrity of tight junctions. We also observed increased levels of mucin and intestinal trefoil factor among TgM9 mice in CAC. We also found that MMP9 expressing CaCo2BBE cells had increased expressions of EGFR and nuclear transcription factor- specificity protein 1 (Sp1). These data imply that MMP9 acts as a tumor suppressor in CAC by sustaining the epithelial mucosal integrity due to the activation of EGFR-Sp1 signaling pathway.