Temporal transcriptional, metabolic, and functional re-programming of THP-1 macrophages by the Lactobacillus rhamnosus R0011 secretome

Abstract

Abstract Macrophage responses to activation are fluid and dynamic and their ability to respond appropriately to subsequent challenge is integral to host defence. Recent evidence suggests that bacteria influence macrophage differentiation and subsequent polarization into pro-inflammatory (M1) and immunoregulatory (M2) phenotypes through direct interactions. However, many questions surround indirect communication mechanisms mediated through secretomes derived from gut bacteria, such as lactobacilli. We examined the effects of secretome-mediated conditioning on macrophage phenotype, focusing on the ability of the Lactobacillus rhamnosus R0011 secretome (LrS) to drive macrophage polarization and to prime responses to subsequent challenge with lipopolysaccharide (LPS). Transcriptional profiling revealed increased M2-associated gene transcription (IL10R, CD36, CD163, TLR1, and TLR8) in response to LrS conditioning. Cytokine and chemokine profiling confirmed these results, indicating increased M2-associated chemokine and cytokine production (IL-10, CCL1, 17, 20, CXCL1 and 2). Metabolite utilization assays indicated diminished reliance on glycolysis for energy generation, coupled with increased phagocytic capacity, characteristics of functional M2 activity. LPS challenge of LrS-conditioned THP-1s revealed heightened responsiveness, indicative of innate immune priming. Overall, the LrS conditions THP-1s into M2 macrophages and primes responses to subsequent LPS challenge. Secretome conditioning of macrophages to respond robustly to inflammatory challenge within an M2 phenotype is an uncharacterized and potentially important route through which lactobacilli can train innate immunity.