Transcriptomic signature and metabolic programming of bovine classical and nonclassical monocytes indicate distinct functional specializations

Abstract

Similar to human monocytes, bovine monocytes can be split into CD14+CD16- classical and CD14-CD16+ nonclassical monocytes (cM and ncM, respectively). Here, we present an in-depth analysis of their steady-state transcriptomes, highlighting pronounced functional specializations. Gene transcription indicates that pro-inflammatory and antibacterial processes are associated with cM, while ncM appear to be specialized in regulatory/anti-inflammatory functions and tissue repair, as well as antiviral responses and T-cell immunomodulation. In support of these functional differences, we found that oxidative phosphorylation prevails in ncM, whereas cM are clearly biased towards aerobic glycolysis. Furthermore, bovine monocyte subsets differed in their responsiveness to TLR ligands, supporting an antiviral role of ncM. Taken together, these data clearly indicate a variety of subset-specific functions in cM and ncM that are likely to be transferable to monocyte subsets of other species, including humans.

Comprehensive phenotyping of peripheral blood monocytes in healthy bovine

“…In addition, recent transcriptomic analyses suggest an anti‐inflammatory function of ncM with a role in the activation of T regs and promotion of tissue repair. Furthermore, similar to the antiviral role described for the human counterpart [43], in bovine ncM the expression of genes linked to cytotoxic T cell activation and interferon production together with their strong response to the activation of TLR7/8, would suggest a special antiviral function of this subset [24]. In Table 1, we reported a complete list of all the phenotypic markers available for bovine monocyte subsets at the moment.…”

“…Phenotypic analysis revealed variable expression of several cell surface markers on bovine monocyte subsets [6, 7]. The expression levels of CD172a, CD45 (Figure 2T), and CD43 are higher on intM and ncM [24], whereas CD9 (Table 1, Figure 2P), CD32 (Table 1, Figure 2R), and CD163 [6, 8, 18, 25] highest expression levels are found on cM. Intermediate monocytes express the highest levels of MHC‐II, CD40, CD11c, and CD86 [6, 24].…”

“…The expression levels of CD172a, CD45 (Figure 2T), and CD43 are higher on intM and ncM [24], whereas CD9 (Table 1, Figure 2P), CD32 (Table 1, Figure 2R), and CD163 [6, 8, 18, 25] highest expression levels are found on cM. Intermediate monocytes express the highest levels of MHC‐II, CD40, CD11c, and CD86 [6, 24]. ncM, which are characterized by their smaller size and lower granularity (Figure 1O), show the highest expression levels of CD49d and CD205 [6, 24] but the lowest levels of CD44 (Figure 2S), compared to cM and intM.…”

“…Intermediate monocytes express the highest levels of MHC‐II, CD40, CD11c, and CD86 [6, 24]. ncM, which are characterized by their smaller size and lower granularity (Figure 1O), show the highest expression levels of CD49d and CD205 [6, 24] but the lowest levels of CD44 (Figure 2S), compared to cM and intM. No expression was demonstrated for CD5, CD13, CD25, and CD209 antigens in the three subsets (Table 1).…”

Uncovering the Gene Regulatory Networks Underlying Macrophage Polarization Through Comparative Analysis of Bulk and Single-Cell Data

“…Some genes displayed delayed response to stimuli, highlighting the dynamic nature of polarization. For instance, cytokine CCL7 only showed higher expression in M1 compared to M2 at 24 hours after stimuli, whereas CLECL1 gene that has been shown to stimulate IL-4 production in T helper cells and is overexpressed in nonclassical monocytes (M2) (Talker et al, 2020) comes up later in M2 polarization at 24 hours. Therefore, distinct subsets of M1-and M2-specific genes were regulated at early, intermediary and late polarization stages.…”