Phenotypic Changes in Macrophage Activation in a Model of Nonalcoholic Fatty Liver Disease using Microminipigs

Aim: Non-alcoholic fatty liver disease (NAFLD) is one of the most common chronic liver disorders associated with metabolic syndrome, and its prevalence has been on the rise. The pathogenesis of NAFLD has not yet been sufficiently elucidated due to the multifactorial nature of the disease, although the activation of macrophages/Kupffer cells is considered to be involved. We previously reported an animal model of NAFLD using Microminipigs (TM) (µMPs) fed high-fat diets containing cholesterol with or without cholic acid. The aim of this study was to investigate the phenotypic changes of macrophages that occur during the development of NAFLD. Methods: Immunohistochemistry of macrophages, lymphocytes, and stellate cells was performed using liver samples, and the density of positive cells was analyzed. Results: The number of Iba-1-positive macrophages increased with increasing cholesterol content in the diet. The numbers of CD163-positive macrophages and CD204-positive macrophages also increased with increasing cholesterol content in the diet; however, the proportion of CD204-positive macrophages among Iba-1-positive macrophages was significantly reduced by cholic acid supplementation. Conclusion: The results suggest that lipid accumulation induced macrophage recruitment in swine livers, and that the number of M2-like macrophages increased at the early stage of NAFLD, while the number of M1-like macrophages increased at the late stage of NAFLD, resulting in a liver condition like non-alcoholic steatohepatitis. We provide evidence of the phenotypic changes that occur in macrophages during the development of NAFLD that has never been reported before using µMPs.