Abstract
Background: One quarter of global adults by overeating and reduced physical activity cause nonalcoholic fatty liver, and progress to nonalcoholic steatohepatitis (NASH), in which 10% of cases lead to liver cirrhosis and/or hepatocellular carcinoma. Adequate therapeutic option is urgent. We previously reported that matrix metalloproteinase-1 (MMP-1) expression in monocytes (MCs) and other types of cells in NASH livers is associated with disease progression. To test the hypothesis that bone marrow-derived monocytes (BMMCs) secrete exosomes with MMP-1 before their infiltration into steatosis liver, we examined MMP-1 mRNA and protein expression in circulating BMMCs. Methods: Twenty-nine NASH patients and 26 non-NASH patients were recruited in this study. Confocal laser scanning microscopic (CLSM) and immune-electron microscopic examinations (IEM), and fluorescence-activated cell sorting of CD34+ BMMCs were performed. Peripheral CD45+CD14+CD34+ cells were co-cultured with steatosis hepatocytes (HCs) isolated from NASH liver. Findings: IEM revealed that MCs were the earliest to acquire an MMP-1-expressing phenotype amongst all investigated cell types. CLSM showed that MMP-1 expression in Kupffer cells, hepatic stellate cells, progenitor cells, HCs, and endothelial cells were observed in subsequent to MCs. In advanced stage of NASH, OV-6- or CK19-positive hepatic progenitor cells around lethal HCs showed strong staining for MMP-1. These results suggested that MMP-1 expressed in progenitor cells may contribute to regeneration of injured liver, while MMP-1 up-regulation in hepatic stellate cells caused their activation leading to fibrosis. Unlike our initial hypothesis, circulating BMMCs did not express significant amounts of MMP-1 mRNA or protein before their infiltration into steatosis liver. By contrast, co-culture with steatosis HCs induced MMP-1 expression in otherwise MMP-1-negative CD34+ BMMCs. This phenotypic change in MMP-1 expression was the most pronounced in CD45+CD14+CD34+ cells. Interpretation: The results of the present study implicated MMP-1 expression by the monocyte progenitor cell population after their migration into steatosis liver in NASH pathogenesis. Funding Statement: This work is supported by grant no. IUHW 2016-24 and -25 from Mr. Takeshi Mori and Mrs. Eiko Mori to Dr. Okazaki. Declaration of Interests: The authors have declared that no conflict of interest exists. Ethics Approval Statement: The study protocol was approved by the Ethics Committee of IUHW (13-B-136, February 22, 2016; 13-B-205, November 24, 2016; 13-B-229, April 27, 2017). All patients provided written formal informed consent for participation in this study.
Published Version
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