Human macrophage polarization in the response to Mycobacterium leprae genomic DNA

Abstract

Infection with Mycobacterium leprae, the causative organism of leprosy, is still endemic in numerous parts of the world including the southwestern United States. The broad variation of symptoms in the leprosy disease spectrum range from the milder tuberculoid leprosy (paucibacillary) to the more severe and disfiguring lepromatous leprosy (multibacillary). The established thinking in the health community is that host response, rather than M. leprae strain variation, is the reason for the range of disease severity. More recent discoveries suggest that macrophage polarization also plays a significant role in the spectrum of leprosy disease but to what degree it contributes is not fully established. In this study, we aimed to analyze if different strains of M. leprae elicit different transcription responses in human macrophages, and to examine the role of macrophage polarization in these responses. Genomic DNA from three different strains of M. leprae DNA (Strains NHDP, Br4923, and Thai-53) were used to stimulate human macrophages under three polarization conditions (M1, M1-activated, and M2). Transcriptome analysis revealed a large number of differentially expressed (DE) genes upon stimulation with DNA from M. leprae strain Thai-53 compared to strains NHDP and Br4923, independent of the macrophage polarization condition. We also found that macrophage polarization affects the responses to M. leprae DNA, with up-regulation of numerous interferon stimulated genes. These findings provide a deeper understanding of the role of macrophage polarization in the recognition of M. leprae DNA, with the potential to improve leprosy treatment strategies.

Keywords: Leprosy; Macrophage polarization; Mycobacterium leprae; RNAseq.

Graphical abstract

Fig. 1

Leprosy spectrum and mechanisms of pathogenesis. From least to most severe: tuberculoid (TT), intermediate borderline tuberculoid (BT), borderline borderline (BB), borderline lepromatous (BL), lepromatous leprosy (LL). Macrophage polarization: M1 showing granulomas and M2 displaying “foamy” macrophages. Boxes depict the cytokine profile in the clinical pole of disease.

Fig. 2

(A) Venn diagram of the number of DE genes in human macrophages across the DNA from strains NHDP (Yellow), Thai-53 (Blue), and Br4923 (Green) used for stimulation. (A) M1, (B) M1activated and (C) M2 macrophages. All DE genes comprise those whose fold change is greater than 2 and adjusted p-value less than 0.05 in each NHDP, Thai-53, and Br4923.

Fig. 3

Venn diagrams comparing the DE genes after M. leprae DNA strain stimulation for compared to M1a against M1 (magenta) and M2 (cyan) (absolute fold change value >2 and an adjusted p-value <0.05). A:M. leprae Br4923, B:M. leprae NHDP and C:M. leprae Thai-53 DNA stimulation.

Fig. 4

Heat Map indicating DE genes in polarized macrophages. A. M1a compared to either M1 or M2 macrophages upon stimulation with either NHDP or Tha-53 DNA but downregulated by stimulation with the other strain. B. Heat map showing DE expression switches within a strain treatment. Genes are listed on the right-hand size. Green represents up-regulation and red represents down-regulation. C. Network analysis of genes presented in A.

Fig. 5

Network analysis of DE genes presented in M1 macrophages upon stimulation with genomic DNA M.leprae strain Thai-53. A. Highly correlated genes in pairwise gene expression. B Genes that were upregulated together in a similar manner shown as connected nodes in the network. C Detail of B.

Fig. 5

Network analysis of DE genes presented in M1 macrophages upon stimulation with genomic DNA M.leprae strain Thai-53. A. Highly correlated genes in pairwise gene expression. B Genes that were upregulated together in a similar manner shown as connected nodes in the network. C Detail of B.

Fig. 5

Network analysis of DE genes presented in M1 macrophages upon stimulation with genomic DNA M.leprae strain Thai-53. A. Highly correlated genes in pairwise gene expression. B Genes that were upregulated together in a similar manner shown as connected nodes in the network. C Detail of B.

Fig. 6

Network analysis of DE genes presented in M1 activated macrophages upon stimulation with genomic DNA M.leprae strain Thai-53. A. Highly correlated genes in pairwise gene expression. B. Genes that were upregulated together in a similar manner shown as connected nodes in the network. C. Detail of B.

Fig. 6

Network analysis of DE genes presented in M1 activated macrophages upon stimulation with genomic DNA M.leprae strain Thai-53. A. Highly correlated genes in pairwise gene expression. B. Genes that were upregulated together in a similar manner shown as connected nodes in the network. C. Detail of B.

Fig. 6

Network analysis of DE genes presented in M1 activated macrophages upon stimulation with genomic DNA M.leprae strain Thai-53. A. Highly correlated genes in pairwise gene expression. B. Genes that were upregulated together in a similar manner shown as connected nodes in the network. C. Detail of B.

Fig. 7

Network analysis of DE genes presented in M2 macrophages upon stimulation with genomic DNA M.leprae strain Thai-53. A. Highly correlated genes in pairwise gene expression. B Genes that were upregulated together in a similar manner shown as connected.

Fig. 7

Network analysis of DE genes presented in M2 macrophages upon stimulation with genomic DNA M.leprae strain Thai-53. A. Highly correlated genes in pairwise gene expression. B Genes that were upregulated together in a similar manner shown as connected.