Abstract Rationale The host-protective role of alpha-1-antitrypsin (AAT) against mycobacteria may be due, in part, to its binding to the cytoplasmic glucocorticoid receptor (GR). We theorized that this binding may regulate gene expression in macrophages, which could impact outcome in infectious diseases. The AAT-GR complex was found to be significantly responsible for limiting Mycobacterium avium complex (MAC) burden in macrophages; this host-protective function of AAT-GR is due, in part, through induction of COLONY STIMULATING FACTOR-2 (CSF-2) gene which encodes for granulocyte-monocyte colony stimulating factor (GM-CSF). Methods To better understand the role that AAT-GR binding impacts gene expression during mycobacterial infection, we performed bulk RNA sequencing (RNA-seq) on four different groups of cells: (i) control THP-1 cells (THP-1control); (ii) THP-1control cells infected with Mycobacterium intracellulare (MAC); (iii) THP-1control cells incubated with MAC + AAT; and (iv) THP-1 cells knocked down for GR (THP-1GR-KD) - by shRNA-lentiviral technology - incubated with MAC + AAT. Results Our analyses revealed that MAC infection significantly upregulates 1,977 genes and significantly downregulates 2,303 genes in THP-1control cells. Additionally, we showed that AAT significantly upregulated 1,200 genes and significantly downregulated 890 genes in MAC-infected THP-1control cells. We next compared these results with those from THP-1GR-KD cells and found that the downregulation of 1,624 genes in THP-1control cells incubated with MAC + AAT were attenuated in THP-1GR-KD cells (indicating that inhibition of these genes by MAC + AAT is dependent on GR). Furthermore, upregulation of 1,683 genes in THP-1control cells incubated with MAC + AAT were attenuated in THP-1GR-KD cells (indicating that activation of these genes by MAC + AAT is dependent on GR). MAC also induced both CSF-2 (GM-CSF) and CSF-1 (encodes for monocyte colony stimulating factor, M-CSF) expression. Whereas AAT inhibited MAC-induced M-CSF expression in a GR-independent mechanism, AAT did not inhibit MAC-induced GM-CSF expression. Conclusions The ability of AAT to induce GM-CSF and to inhibit MAC-induced M-CSF may skew macrophages to a phenotype that is better endowed to control mycobacterial infection. This abstract is funded by: None
Chan et al. (Fri,) studied this question.