Defining the role for polyamines in cholestatic liver disease

About This Grant

PROJECT SUMMARY: Biliary atresia (BA) is a cholestatic liver disease of infancy that remains the leading indication for pediatric liver transplantation. BA is characterized by pro-inflammatory immune cell activation, macrophage (M) infiltration, and accumulation of dead/apoptotic cells. The persistence of apoptotic cells in the tissue environment leads to the release of pro-inflammatory danger signals and ongoing liver injury. Ms are heterogeneous and plastic cells that play a critical role in minimizing tissue inflammation through apoptotic cell removal (i.e. efferocytosis), however, evidence suggests that this function is impaired in BA. Polyamines are specific metabolites known to both promote M efferocytosis and limit M inflammatory polarization, however, the ability for polyamines to regulate M function and improve disease outcomes in BA have not been established. We will overcome this gap in knowledge in the current proposal. We have previously identified a subset of MERTK+ Ms in human BA that differed from other disease subsets by increased expression of genes involved in efferocytosis. We have also identified a transcriptionally similar M subset to these human MERTK+ Ms in the Rhesus rotavirus-induced murine model of BA. However, murine BA MERTK+ Ms showed decreased efferocytosis activity when compared to saline controls suggesting impaired efferocytosis in disease. In parallel with these data, we demonstrated that increased serum levels of spermidine and putrescine in human BA patients at diagnosis was associated with improved outcomes and spermidine administration in murine BA reduced the severity of liver injury. Based on this preliminary data we hypothesize that supplemental polyamines can reduce hepatic injury in BA through both stimulation of M efferocytosis and reprogramming Ms to an anti-inflammatory phenotype. We will investigate our hypothesis through 1) defining the mechanism by which spermidine promotes anti- inflammatory M polarization, 2) determining the role for putrescine in regulation of M efferocytosis, and 3) evaluating the cell-specific mechanism by which polyamine synthesis reduces liver injury and improves disease outcome in BA. Our innovative research plan uses complimentary in vivo and in vitro methods in murine models of obstructive cholestasis and primary Ms isolated from pediatric patient livers. We anticipate that synergistic administration of spermidine and putrescine will result in the greatest improvement in disease outcomes and lay the foundation for future therapeutic clinical trials using polyamines to prolong transplant-free survival in BA.