Cellular and Molecular Changes Impacting Cancer Progression in Non-Alcoholic Fatty Liver Disease

Abstract

Non alcoholic fatty liver disease (NAFLD), is recognized as the one of the most common causes of liver disease in the United States and worldwide. NAFLD is associated with increased risk of development of hepatocellular carcinoma. Additionally, our lab has shown an increased metastatic burden in the steatotic liver using a mouse model of diet induced steatosis. NAFLD is characterized by cellular and molecular changes in the liver which include an influx of inflammatory cells, changes in gene expression and alteration in cytokine production. We hypothesize that changes in the steatotic liver contribute to a more permissive microenvironment for tumor growth and establishment of metastases. To better understand the alterations to the liver with NAFLD, we used a murine model of steatosis and corroborated our results with human samples of NAFLD. Analysis of inflammatory cell populations revealed increased infiltration of CD11b positive myeloid and CD3 positive lymphocytic cell populations in steatotic livers compared to normal livers. Significant alterations in cytokine profiles in the plasma and liver tissue lysates from normal and steatotic mice were detected including leptin, CXCL1, CXCL2, and CXCL16 that were further shown to directly increase hepatocyte proliferation in vitro. To determine molecular factors altered with NAFLD, we assessed changes in matrix metalloproteinase levels and show that MMP13, an interstitial collagenase, is significantly upregulated in the steatotic liver. To evaluate the role of host MMP13 on tumor development, we used the splenic injection model of liver metastasis in mice genetically deficient in MMP13 and show a significant decrease in metastatic tumor burden in MMP13-/- mice compared to wildtype mice. Using confocal microscopy we observed a significant decrease in the number of individual tumor cells extravasating from the hepatic vasculature in MMP13-/- mice compared to wildtype mice. Stable MMP13 knockdown cell lines were used to demonstrate that reduced tumor derived MMP13 decreased migratory and invasive properties in vitro and decreased metastatic burden in vivo. This study identifies changes in the steatotic liver that impact tumor development and establishment of metastases in the steatotic liver microenvironment.