Abstract 389: MMP12 and myeloid cell populations influence establishment of tumor metastases in the steatotic liver microenvironment

Abstract

Introduction: Non-alcoholic fatty liver disease (NAFLD), encompassing steatosis and progression to non-alcoholic steatohepatitis (NASH) are liver disorders of increasing clinical significance. Studies in our lab have shown that hepatic steatosis establishes a permissive microenvironment for metastatic tumor seeding and tumor progression in the liver. To understand the molecular factors influencing the initial survival and growth of tumors in the steatotic liver microenvironment, we adopted a candidate approach and performed microarray analysis to compare RNA from normal vs steatotic liver samples in mice. MMP12 (macrophage metalloelastase) was identified as an important proteinase associated with the microenvironments of hepatic steatosis and steatohepatitis. MMP12 can influence immune-mediated injury response by processing latent TNF alpha and regulating neutrophil infiltration, cytokine release as well as macrophage recruitment. We hypothesize that increased MMP12 levels in the steatotic liver contribute to a more permissive microenvironment for primary tumor growth and establishment of metastases by alteration of inflammatory cell populations. Results: Realtime qPCR anlaysis verified a significant increase in MMP12 expression in murine steatotic livers compared to normal control livers. In a splenic injection model, hepatic metastases in steatotic MMP12 deficient livers were significantly reduced as compared to hepatic metastases in steatotic wildtype livers. Flow cytometric analysis demonstrated an alteration in the level of Gr-1 positive inflammatory cell populations in the steatotic livers of both wildtype and MMP12 deficient livers when compared to normal nonsteatotic livers. Although no significant changes were observed in the percentage of F4/80 positive macrophage population, using immunohistochemistry we did observe accumulation of F4/80 positive macrophages into crown-like structures within steatotic MMP12 deficient livers. To determine whether the inflammatory cells in the liver microenvironment were contributing to survival of tumor cells, we performed an in vitro co-culture assay of syngeneic MC38 tumor cells with either CD90.2 cells (pan T cells) or CD11b cells (macrophages/monocytes). Fewer numbers MC38 cells were present 3 days after co-culture with CD11b cells from MMP12 deficient mice, which was corroborated with decreased luciferase measurements from MC38-luc tagged cells. Conclusions: These results suggest a role for MMP12 in mediating the inflammatory response accompanying tumor establishment in the steatotic liver microenvironment. The molecular mechanisms by which MMP12 influences a decrease in metastatic tumor burden in the setting of fatty liver disease are currently being investigated. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 389. doi:1538-7445.AM2012-389