Role of Neutrophils in the Pathogenesis of Cholangiopathies - Cholangiopathies are responsible for significant morbidity and mortality but remain the least understood diseases in hepatology. Cholangiocytes are the main cellular target in cholangiopathies and in response to damage or inflammation, they assume a reactive phenotype, generate pro-inflammatory mediators and cyto-chemokines, proliferate, reduce their secretory function, and further amplify the inflammatory responses. The inflammatory microenvironment in cholangiopathies is populated by several cell types that communicate with each other and with cholangiocytes. This complex cellular network is still poorly understood and exhibits disease-specific aspects that may ultimately be relevant for therapy. Among the inflammatory cells infiltrating the portal space, neutrophils have received little attention. Some disorders affecting bile ducts result in significant infiltration of neutrophils into the portal region, but the pathophysiological consequences remain unknown. The field of neutrophil biology has recently advanced in a fundamental way. There is now a recognition that some neutrophils are attracted to and then reprogrammed by tissues in an organ-specific fashion. In contrast to those in the bloodstream, these infiltrating neutrophils often live days longer in target tissues, where they go on to serve nondestructive roles such as regulation of metabolism, secretion, angiogenesis, and proliferation. Although these non-traditional roles for neutrophils have not yet been studied in cholangiopathies, in part due to difficulties (that we have overcome) in isolating neutrophils from liver in sufficient amounts for single cell transcriptomic analysis. Our preliminary evidence suggests that periductular neutrophils are largely distinct from those of neutrophils in the bloodstream. We also have generated preliminary evidence to suggest that cholangiocytes secrete cytokines/chemokines as ‘homing signals’ to attract and then reprogram neutrophils, and these homing signals may differ depending on the cholangiopathy. To make these observations, we have developed several methods for recovering neutrophils from the liver and from the biliary tree in sufficient amounts to perform scRNA-seq. Based on extensive new preliminary data, we hypothesize that neutrophils play a major role in the pathogenesis of cholangiopathies by being attracted by cholangiocytes, which reprogram the neutrophils to amplify the inflammatory response and to interact with cholangiocytes resulting in cholestasis, changes in transcriptome and altered proliferation in a condition--specific way. The nontraditional roles for neutrophils being proposed here will be paradigm-shifting in terms of how we understand the role of neutrophils in biliary diseases. Furthermore, we will advance the field of neutrophil biology as well, by providing evidence not only that transcriptomic signatures of neutrophils in the liver differ from those in the blood, that these signatures in the liver may be disease-specific and that the interactions between cholangiocytes and neutrophils are targets of potential therapeutic relevance.
