Endogenous beta-galactosidase activity marks TREM2-expressing Kupffer cell population in the livers of carbon tetrachloride-treated Lgr5-LacZ mice

Lgr5+ cells isolated from liver organoids act as bipotent liver progenitors. Beta-galactosidase (beta-gal)-expressing cells appear in injured livers of Lgr5-LacZ mice, however, their origin and identity has remained controversial. Here we sought to clarify this issue. The majority of beta-gal+ cells emerged in pericentral regions of the liver lobule. Lineage tracing demonstrated that beta-gal+ cells did not originate from hepatocytes or cholangiocytes. Beta-gal+ cells were negative for hepatocyte and cholangiocyte markers; but positive for Kupffer cell markers. Transcriptome analysis revealed the expression of endogenous beta-galactosidase Glb1 and genes characteristic of TREM2+ macrophages that may regulate stem cell maintenance. We were not able to detect the expression of the Lgr5-LacZ transgene and concluded that the transgene was silenced. Overall design: Lgr5-LacZ transgene-bearing mice (aged 7-12 weeks) were subjected to liver injury by single intraperitoneal injection of CCl4 (1µl/g body weight) diluted in rapeseed oil. Liver samples were collected 6 days after the injection. We analysed the transcriptional profiles of sorted b-gal+ F4/80high cells (sample name FITCpos), b-gal- F4/80high cells (sample name FITCneg), EpCAM+ cholangiocytes and hepatocytes (HEP). Each sample contains pooled cells from 2 individual mice.