Project 2: Cytoplasmic chromatin fragments (CCF) as a driver of liver cancer and target for intervention during aging

PROJECT SUMMARY – PROJECT 2 The incidences of liver cancer (primarily hepatocellular carcinoma (HCC)) are increasing and disease outcome is poor. Consequently, there is an urgent need for new therapies and preventive strategies. Age is a major risk for HCC and non-alcoholic fatty liver disease (NAFLD). NAFLD is a chronic liver disease that encompasses a progressive range of disorders of increasing severity and risk of HCC, from benign fatty liver (steatosis), to inflammatory non-alcoholic steatohepatitis (NASH), fibrosis and cirrhosis. Aging is accompanied by many molecular, cellular and tissue changes that are candidate drivers of NAFLD and HCC, including the “hallmarks of aging” that are dysregulated with age in diverse tissues and organisms; for example, changes to mitochondria, metabolism, the epigenome, accumulation of senescent cells, inflammation and immune changes. Cell senescence is caused by a range of cellular stresses and characterized by an irreversible proliferation arrest and a potent pro-inflammatory phenotype, the senescence-associated secretory phenotype (SASP). Recently, we showed that in senescent cells, mitochondria dysfunction signals to evict fragments of chromatin from the nucleus into the cytoplasm (cytoplasmic chromatin fragments (CCF)) via a nucleus-to- cytoplasmic blebbing process. CCF are sensed by the anti-viral cytoplasmic DNA sensing apparatus to activate NFkB and the SASP. The SASP of senescent cells includes interferons, a family of cytokines involved in cell intrinsic anti-viral mechanisms, control of cell proliferation, inflammation and adaptive immunity, and tumor suppressive and oncogenic processes. Although SASP and acute IFN signaling have important benefits, chronic SASP and IFN signaling can be detrimental. As a source of chronic inflammation, SASP promotes tissue aging and disease, including liver cancer. Chronic IFN signaling can promote immunosuppression, in part by upregulation of immune checkpoint inhibitors, such as PD-L1. Based on unpublished data, we hypothesize that accumulation of CCF in aged and/or senescent liver hepatocytes drives chronic activation of IFN signaling, expression of IFN target genes and immune checkpoint inhibitors, such as PD-L1. We further hypothesize that this, in turn, generates an immunosuppressed liver microenvironment that is permissive for transformation of old hepatocytes. By antagonizing this immunosuppressive signaling pathway, we hypothesize that several different types of intervention can prevent liver cancer during aging. Completion of these Specific Aims will promote novel interventions to prevent HCC.