Vitamin D modulates human macrophage response to Mycobacterium tuberculosis DNA.

Mycobacterium tuberculosis (Mtb) is a facultative intracellular pathogen that infects macrophages where it avoids elimination by interfering with host defense mechanisms, including phago-lysosome fusion. Endosomal Toll-like receptors (TLRs) generate Type I Interferons (IFNs), which are associated with active tuberculosis (TB). We aimed to explore if DNA from different Mtb lineages lead to differences in the inflammatory response of human monocytic/macrophage cells. THP-1 cells which express two inducible reporter constructs for interferons (IFNs) as well as for NF-κB, were stimulated via endosomal delivery of Mtb DNA as a nanocomplex with PEI. DNA from different Mtb phylogenetic lineages elicited differential inflammatory responses in human macrophages. An initial relatively weak IRF-mediated response to DNA from HN878 and H37Rv increased if the cells were pre-treated with Vitamin D (Vit D) for 72 h. RNAseq of THP-1 under different transformation conditions showed that pre-treatment with Vit D upregulated several TLR9 variants, as well as genes involved in inflammatory immune response to infection, immune cell activation, Type I IFN regulation, and regulation of inflammation. Vit D appears to be important in increasing low IRF responses to DNA from certain lineages of Mtb. Variations in the IRF-mediated response to DNA derived from different Mtb genotypes are potentially important in the pathogenesis of tuberculosis since Type I IFN responses are associated with active disease. The role of Vit D in these responses could also translate into future therapeutic approaches.

Alternative splicing analysis in human monocytes and macrophages reveals MBNL1 as major regulator.

We report the detailed transcriptomic profiles of human innate myeloid cells using RNA sequencing. Monocytes migrate from blood into infected or wounded tissue to differentiate into macrophages, and control inflammation via phagocytosis or cytokine secretion. We differentiated culture primary monocytes with either GM- or M-CSF to obtain pro- or anti-inflammatory macrophages, and respectively activated them with either LPS/IFNγ or anti-inflammatory cytokines. We also treated the THP-1 monocytic cell line with PMA and similar cytokines to mimic differentiation and activation. We detected thousands of expression and alternative-splicing changes during monocyte-to-macrophage differentiation and activation, and a net increase in exon inclusion. MBNL1 knockdown phenocopies several alternative-splicing changes and strongly impairs PMA differentiation, suggesting functional defects in monocytes from Myotonic Dystrophy patients. This study provides general insights into alternative splicing in the monocyte-macrophage lineage, whose future characterization will elucidate their contribution to immune functions, which are altered in immunodeficiencies, autoimmunity, atherosclerosis and cancer.