MSC−sEV Treatment Polarizes Pro−Fibrotic M2 Macrophages without Exacerbating Liver Fibrosis in NASH

Mesenchymal stem/stromal cell small extracellular vesicles (MSC−sEVs) have shown promise in treating a wide range of animal models of various human diseases, which has led to their consideration for clinical translation. However, the possibility of contraindication for MSC−sEV use is an important consideration. One concern is that MSC−sEVs have been shown to induce M2 macrophage polarization, which is known to be pro−fibrotic, potentially indicating contraindication in fibrotic diseases such as liver fibrosis. Despite this concern, previous studies have shown that MSC−sEVs alleviate high−fat diet (HFD)−induced non−alcoholic steatohepatitis (NASH). To assess whether the pro−fibrotic M2 macrophage polarization induced by MSC−sEVs could worsen liver fibrosis, we first verified that our MSC−sEV preparations could promote M2 polarization in vitro prior to their administration in a mouse model of NASH. Our results showed that treatment with MSC−sEVs reduced or had comparable NAFLD Activity Scores and liver fibrosis compared to vehicle− and Telmisartan−treated animals, respectively. Although CD163(+) M2 macrophages were increased in the liver, and serum IL−6 levels were reduced in MSC−sEV treated animals, our data suggests that MSC−sEV treatment was efficacious in reducing liver fibrosis in a mouse model of NASH despite an increase in pro−fibrotic M2 macrophage polarization.