Myeloid cell-expressed heme oxygenase-1 mitigates liver injury and fibrosis via the ligand of numb-protein X1 (LNX1)-Notch1 pathway

Activation of resident macrophages (Mf) and hepatic stellate cells in the perisinusoidal space is a key event in chronic liver injury. Under these circumstances, dysregulated innate immunity and inflammatory processes drive progressive accumulation of collagen, resulting in scarring and eventually, cirrhosis with life-threatening complications. In summary, by using RiboTag-based sequencing, we identified a novel regulatory LNX1/Notch1 pathway downstream of HO-1 that drives a protective form of M2 polarization of Mf and inhibits expansion of reactive cholangiocytes and liver fibrosis. Overall design: To investigate the role of HO-1+ Mf in liver fibrosis progression we subjected Hmox1flfl and LysM-Cre:Hmox1flfl mice to BDL surgery. To understand the mechanisms behind the protective role of M?-expressed HO-1 in the BDL model, we employed the RiboTag technology to specifically analyze the gene expression profile of HO-1-deficient M?. This approach allows efficient isolation of ribosome-associated mRNAs from specific cell types based on Cre-driven expression that drives tissue-specific HA-tagging of ribosomes (Sanz et al., 2009). We bred LysM-Cre:RiboTag mice to Hmox1flfl mice and obtained animals with conditional deletion of HO-1 in myeloid cells and concomitant myeloid-specific ribosome epitope-tagging (LysM-Cre:Hmox1flfl:RiboTag mice)