CD5L is a target of transcription factor Nrf2

CD5 antigen-like (CD5L), also known as apoptosis inhibitor expressed by macrophages (AIM), is a secreted protein produced by macrophages, which has both cell-autonomous and non-autonomous functions: it has been implicated in multiple biological processes, including inflammation, infection, and fibrosis. The transcriptional regulation of CD5L is complex, and a comparison of the proteomes of bone marrow-derived macrophages from mice with graded expression of transcription factor NF-E2 p45-related factor 2 (Nrf2) indicated that Nrf2 controls expression of the CD5L gene. Using genetic and pharmacological means to increase or decrease Nrf2 activity, we found a correlation between the abundance of Nrf2 and CD5L expression in both murine macrophages and primary human monocyte-derived macrophages. Furthermore, the potency of small-molecule Nrf2 activators with distinct mechanisms of action and different potencies, correlated with the extent of CD5L expression, both at the mRNA and the secreted protein levels. Conversely, depletion of Nrf2 resulted in a significant decrease in CD5L mRNA levels. Chip-seq analysis showed Nrf2 binding 20,000 bp upstream of the Cd5l promoter, a region containing sequences resembling the antioxidant response element (ARE, 5'-TGACNNNGC-3') Nrf2-binding motif. Deletion of two of these sequences by CRISPR/Cas9 gene editing led to a profound decrease in CD5L mRNA levels, confirming the critical role of these ARE-like sequences in controlling CD5L expression. Recombinant CD5L (rCD5L) suppressed transforming growth factor β (TGFβ)-directed fibrogenic responses in human lung fibroblasts, suggesting that Nrf2 activators, such as the clinically used omaveloxolone (RTA-408), could protect against pulmonary fibrosis by boosting the levels of CD5L.